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between each other's legs; and the air corrupted by the refpiration of twenty perfons crowded into fo fmall a space occafioned our paffing the bad night of which I have fpoken.

The next day we foon traversed the fecond platform, at the entrance of which we had paffed the night; from thence we afcended to the third, which we likewife foon croffed, and in half an hour came to the great declivity, by which in drawing to the east, we got upon the rock which forms the left fhoulder of the top of Mont Blanc.

At the beginning of this afcent I was out of breath by the rarity of the air; however by refting a moment every thirty or forty paces, but without fitting down fo far recovered my breath, as to be able in about forty minutes to get to the entrance of the avalanche which had fallen the preceding night, and which we had heard from our tent.

There we all stopped for fome minutes in hopes that after having rested our lungs and legs, we fhould be able to get over the avalanche pretty quick and without refting to take breath, but in that we deceived ourfelves, the fort of wearinefs which proceeds from the rarity of the air is abfolutely infurmountable; when it is at its height, the moft eminent peril will not make you move a ftep fafter. But I infufed fresh courage into my guides by repeatedly telling them that this place was really the leaft dangerous, becaufe all the loofe fnow of the heights above us had already come away.

Beyond this avalanche the declivity became continually more floping, and on our left bordered on a frightful precipice; it was neceffary to get over a pretty large opening, the paffage of which was incommoded by a rock of ice, which forced us to the border of the declivity. The foremost guides had cut fteps here and there on the hard fnow as they went on; but as they had left the spaces too long it was necessary to take such long steps that one ran the risk of miffing ones footing, and fliding without remedy to the bottom. At last, towards the top the thawed furface became thinner; then it broke under our feet, and underneath it eight or nine inches of crumbled fnow, which rested on a fecond cruft of hard fnow, into which we funk to the calves of our legs, after which we flided down the fide of the precipice, to which we were only held by the upper cruft, which thus found itself loaded with a great part of the weight of our bodies; and if it had broken we fhould infallibly have flided to the bottom; but I did not think of the danger, my refolution was taken, I determined to go on as long as my ftrength would enable me, and I had no other thought than that of advancing with a firm ftep.

It is faid when you walk on the border of a precipice you fhould not look at it, and is true to a certain point; but the following advice is the refult of my long experience. Before you engage in a dangerous paffage you fhould begin by contemplating the precipice, until you get quite familiar to it, and it has loft its force on the imagination, and you can look at it with a fort of indifference; meantime you should study the way you fhould go, and mark as you may fay your steps: after which the danger is no more thought of, and you only think of following the prescribed way. But if you cannot bear the fight of the precipice and accuftom yourself to it, give up the enterprize, for if the path be narrow, it is impoffible to look where to place your feet without looking at the precipice at the fame time: and this fight if taken unawares dazzles you, and may prove your deftruction; this rule of conduct in danger appears to me applicable to moral as well as natural cafes.

I employed there, and in other dangerous fituations the manner of helping one's-felf by the guides, which appears to me the fureft, for him who employs them, and the leaft inconvenient for those who help him; it is to have a light but strong, ftick, eight or ten feet long; two guides placed the one before and the other behind, keeping the stick by

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the fide of a precipice, the one guide at one end, and the other at the other, and your. felf in the middle, with this walking fence you fupport yourself as occafion requires; this neither incommodes nor tires the guides, and may ferve to fupport themselves in cafe one of them fhould flip or fall into a crevice. It is in this attitude that the Chevalier Mechel has reprefented me in the large coloured plate that he had engraved from our caravan in the middle of the furrounding ices.

At length in two hours and a half, reckoning from the place where we flept, we attained the rock that I call the left fhoulder of the fecond stairs of Mont Blanc. In this place there opened to my view an immenfe horizon and quite new, for the fummit being at our right, nothing concealed from our view the whole of the Alps on the fide of Italy, which I had never before feen from fuch a great height; but I referve this detail for the following chapter. There I had the fatisfaction to fee myself certain of attaining the fummit, fince the remaining afcent was neither very floping nor dangerous. We here stopped to eat a bit, feated on the borders of this magnificent terrace; but the bread and meat we brought with us were frozen; yet the thermometer had never been lower than three degrees below the freezing point, and these aliments, fhut in and covered in a doffer carried on a man's back, ought to have been a little preserved from the cold by the heat of his body. I am perfuaded that on the plain in the fame degree of cold these aliments would not have been frozen, and very likely that there even a thermometer fhut up in a doffer would not be lower than o; but in this rarified and conftantly renewed air, the bodies or fubftances impregnated with water undergo a very great evaporation, and on that account imbibe the cold more than the dry ball of a thermometer: at nine in the morning, the thermometer was at half a degree above 0, and my hygrometer at fifty-nine. The naked rocks that we met there, and which form two forts of black and projecting ridges, which are very well seen from the borders of our lake, to the left of the higheft fummit of Mont Blanc, are of granite, here reduced to fcattered fragments; there, in folid rocks divided by pretty near vertical fiffures, the direction of which is conformable to that which generally reigns in these mountains, that is to fay, from N. E. to S. W., and which in confequence I looked upon as beds.

The felfpar which enters into the compofition of these rocks is white bordering on grey, or on green, or on a reddifh colour; it gives by the blow-pipe a glafs, from which. may be obtained globules of o, 6, transparent, without colour but full of bubbles.

This felfpar is fometimes pure, covered or even mixed with a grey fubftance verging on fea green; without brightnefs, earthy, brittle, ftripped with a grey whitenefs. This fubftance appears to be of an earthy fteatite; it is difficult to get fragments of it free from felfpar; thofe which I have been able to feparate, have melted by the tube into green-glafs, tranflucid and of an extremely fat afpect. They difcolour on the fibres of fappare, and diffolve it with effervefcence.

The whitish half tranfparent quartz, which enters into the compofition of this granite, appears fattifh on breaking; a fragment of a fifteenth of a line in length, by a thirtieth in thickness or of 0,067, on 0,033, fixt at the extremity of a loose thread of fappare, became quite round at the flame of a blow-pipe, in loofing a little of its transparence which under this volume appeared perfect, and formed in itself fome bubbles in its in-terior. This quartz is then more fufible than rock crystal, in the proportion of 0,035

to 0,014.

These granites are frequently mixed with hornblende, fometimes blackish, fometimes bordering on green.

There is also feen here chlorite often of a green colour, fometimes in nefts, and even in thick maffes. It is tender but not crumbly; of a very fine grain, and its small parts feen

feen through a microscope, appears like fmall blades very tranflucid, of a clear green, but they have not the regularity of those of St. Gothard which I have defcribed. This foffile, as well as the hornblende, appears to supply in these granites the place of mica, which only fhews itfelf in very fmall and fcarce blades.

Some of thefe granites appear rotted, there are obferved in them fmall cavities of an angular, irregular form full of a rusty brownish duft. In breaking these granites there is found in their interior parts fmall brown pyrites tarnished on the outfide, but brilliant and of a very pale yellow infide, and whofe fragments are attractable by the loadftone. It is from the mixture of these pyrites that these cavities are formed. My guides found fome fragments of thefe fame granites, in which are feen cubical pyrites of three or four lines in thickness, which on breaking appear very brilliant, and of a brafly high coloured yellow; they do not alter on being expofed to the air.

On these rocks are alfo found fome quartz with fome veins and nefts of delphinite or green schorl of Dauphiné; it is but confufedly cryftalized, but to be diftinguished by its fwelling under the blow-pipe, and the black and refractory scoriæ into which it changes.

In fome places thefe granites degenerate into irregular fchiftofe rocks, formed of quartz and fellpar, without any mixture of mica, and whofe beds are separated and covered with clay of a nut-brown ferruginous colour, and melts into a black glass.

In these fame granite rocks are inclofed a layer of granitel, almoft entirely compofed of black and fhining lamellar hornblende, and of grey felfpar tranflucid, of the colour of rufty iron at its furface.

To conclude, my guides found in these rocks a palaiopetre or primitive petrofilex of a grey colour bordering on green, tranflucid at a line thick and even to 1, 2; fcaly or fhelly on breaking, hard, interiorly mixed with fpots of a deep green, which are fcarcely vifible but by a glafs, and which appear to be of steatile; and alfo with fome fpots of pyrites, which in diffolving ftain of a rufty colour the places near it. This ftone in melting turns to a green glafs like that of felfpar.

After having refted and examined thefe rocks, I refumed my journey about nine o'clock. As I had measured from Chamounie the heights of the parts of the mountain, I knew that I had not more than about one hundred and fifty toifes to go, and that by a declivity of not more than twenty-eight or twenty-nine degrees, on a firm and not flippery fnow, free from crevices, and distant from precipices, I therefore hoped to attain the fummit in lefs than three-quarters of an hour; but the rarity of the air prepared me difficulties greater than I could have foreseen. I have obferved in the abridged relation, that towards the latter end, I was obliged to take breath every fifteen or fixteen fteps; mostly standing fupported on my ftick, but obliged about every third time to fit down; this neceffity of refting was abfolutely infurmountable; I endeavoured to overcome it, my legs failed me, I felt a fwooning, and I was feized with a dazzling quite independent of the power of the light, as the double crape which covered my face perfectly fcreened my eyes. As it was with extreme concern, that I thus faw the time pals that I had hoped to dedicate to the making of my experiments on the fummit, I made feveral attempts to fhorten my rests; I endeavoured for example not to exert my full ftrength, and to ftop at every four or five fteps, but I gained nothing by it; I was obliged at the end of fifteen or fixteen fteps to rest as long as if I had done it without intermiflion, what is remarkable is that I did not feel this great uneafinefs till eight or ten feconds after I gave over walking. The only thing which did me good and increafed my ftrength was the air of the north wind; when in afcending I had my face turned to that fide, and strongly inhaled the air coming from thence; I could without topping go twenty-five or twenty-fix yards.

The

The generality of thefe fenfations felt by the twenty people of which our party was formed, and the details which I have given in my abridged account, cannot leave any doubt refpecting the cause of these phenomena. They befide perfectly agree with what is known as to the neceffity of the air, and even of an air of a certain degree of denfity, for the preservation of animals of a warm nature.

Pretty near the middle of this afcent we paffed near two fmall rocks, projecting over the fnow. The higheft of them had been lately fhattered, and its fragments thrown over the fresh snow to the distance of feveral feet. And as affuredly no body had been there to blow up this rock with powder, or break it with an iron bar, there can be no doubt but it was produced by thunder. Yet I could not discover any glaffy bubble. In the abridged account I have faid that it proceeded from its conftituent parts being extremely refractory; but this is an error, for I have fince then feen fragments from the rocks of the Dome of Gouté, which are exactly of the fame nature of the one now in queftion, and which are covered with glaffy bubbles. This difference proceeds rather from the greater or lefs violence of the ftroke they have received, or of the lefs or greater moisture then contained in them. Among thefe fcattered fragments were feen leaves of granite in maffes more or lefs thick, whofe great faces were pretty near parallel to

each other.

The lower rock prefents the form of an horizontal smooth table, its length from north to fouth fix feet fix inches, and its breadth four feet from east to weft. This table finks into the fnow from above or from the weft; but from the lower fide or from the east its border rifes four feet eight inches fix lines above the fnow. It is a folid block without any vifible feparation. I carefully took its dimenfions that it might be known hereafter if it fhould increafe or diminish.

These rocks, fituated near two thousand four hundred toises above the sea, are interefting on account of their being the highest of our globe examined by naturalifts; Meffrs. Bouguer and Condamine had been on the Cordilleres to an equal and even fome toifes greater height than our rocks (two thoufand four hundred and feventy toifes): they did not underftand ftones, but as they fay they have fent a great many cafes full of fpecimens from the mountains on which their trigonometrical operations had conducted them, I should have been very defirous to have thefe fpecimens examined by judges.

The deceafed Duke of Rochefoucault, a man as much diftinguifhed for his knowledge as his virtues, and who has been the innocent victim to the troubles of a country for which he had made and would ftill have made the greatest facrifices, was willing at my request to examine thefe rocks with the greatest care and attention, either at the Jardin du Roi or at the Academy of fciences, of which he was a member, but he could neither find them nor gain any intelligence of what was become of them.

The scarcity of fpecimens of rocks fituated fo high, and the confequences that might be drawn from their nature in different fyftems of geology, engage me to give a particular description.

They are granite in mafs, where hornblende and steatite take the place of mica, which is there rare, a bright fun and a magnifying glafs are neceffary to be able to diftinguish fome white and bright fcales; it is even doubtful if thefe brilliant particles, which it is impoffible to take off, are really mica.

Felfpar is the prevailing part of thefe granites; it evidently forms about the three fourths of their mafs. Their cryftals, pretty near parallelopepid, vary in fize; fome are feen an inch in length and fix lines broad, They They are of a dull white, feebly tranflucid, of little luftre, of the fort I call dry; they yield by the blow pipe a transparent glass, but with bubbles, of which may be formed balls of o, 81, and of confequence fufible at 70 degrees of Wedgwood. On the filet of fappare the bubbles diffipate, and there remains a

tranfparent

transparent milky glafs, which fubfides without penetrating or diffolving. Thefe cryftals of felfpar appear here and there of a tarnished green, caufed by a flight mixture of fteatite which covers them.

The quartz which forms a little lefs than the fourth of the mafs, is grey bordering on violet; uneven in breaking, brilliant in places, not scaly but conchoid. Its fufibility is pretty near the fame as that of other granitic quartz.

The hornblende, which forms too fmall a portion to be of much account, is black bordering on green; it fhews fome tendency to a fcaly and brilliant form, but is oftenest twinkling and almoft earthy. It fufes into a black bright glafs, cavernous in its interior, and which on the thread of fappare paffes to a bottle brownish green, changes colour afterwards, and diffolves with fome effervefcence which proves a mixture of magnetical earth.

The earthy fteatite likewife forms a very fmall part of thofe granites.

All thefe granites have their natural divifions covered with a green or black cruft. This is an earth resembling the chlorite, of a blackish green, fhining a little at its exterior furface, but of a clearer and more earthy green in the fractures, brittle, the streak greyish green, turning brown under the blow-pipe, then giving a button = 0, 3, or fufible at the 189th degree of Wedgwood. This button has a metallic afpect, a little unequal, and of a little tarnifhed or iron melted colour; and not only this button but all the parts that the power of the flame has made brown, are very strongly attractable by the loadstone. A small fragment tried on the filet of fappare, infiltrates immediately like ink into the pores, then turns to a tarnished brown, and at length entirely lofes its colour, but without appearance of diffolution.

The green cement which covers other parts of this granite in their fpontaneous divifions is lefs obfcure, fhining enough, tranflucid, foft and a little greafy to the touch, brittle and easily streaked into grey, changing by the blow pipe into a tranflucid glass, which becomes tranfparent on the filet of fappare, and diffolves it, but without ebullition. This cement appears to be of the nature of iteatite; I was not able to procure any pieces large enough to measure its fufibility.

The latter part of the ascent between these little rocks and the fummit was, as might be fuppofed, the most difficult for the respiration; but at length I gained the long wifhed for point. As during the two hours this painful afcenfion coft me, I always had under my eyes almost every thing to be feen from the fummit, my arrival on it was not at tended with that furprise one might imagine. The greatest pleasure I felt was that of seeing my great uneafinefs at an end; for the length of this ftruggle, the recollection of the ftill poignant fenfations the difficulties this victory had coft me, caufed me a great deal of irritation. The moment I had got to the highest top of the fnow with which this fummit is crowned, I trod upon it with a fort of anger rather than felt a fentiment of pleafure. Befides my object was not folely the getting to the top; I wanted there to make obfervations and experiments which would make this undertaking valuable; and I was very much afraid I could make but a very small part of what I had propofed; for I had already found even on the platform where we flept, that all experiments attended with care, caused fatigue in this rarified air, and that because without thought you hold your breath; and as it is neceffary to fupply the rarity of the air by the frequency of refpir ation, this fufpenfion caused a fenfible uneafinefs, and I have been under the neceffity of refting and taking breath after having obferved an inftrument of any fort, as one should do after having got up a fteep hill. Still the fight of the mountains gave me a fenfible fatisfaction, of which a more particular account will be feen in the following chapter. But before the contemplation of thofe diftant objects I fhould fay a word of the form of this fummit, and finish the defcription of the rocks nearest to it.

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