was excited by it; fo that it is reafonable to fuppofe, that, if precisely the fame degree of friction were given to both the parts, no contractions would ever be produced by them, when used in this way. The fecond is, that, although only one part of the metal be rubbed, ftill, if both the muscle and nerve be coated with fome other metal, the application of the rubbed metal between thefe fimilar coatings will not be followed -by motions; which, however, will immediately be produced, by touching the naked muscle and nerve with the fame piece of metal. But, whether any part of my reafoning upon this head be admitted as juft or not, it must yet be granted, as I think I cannot be mistaken refpecting the facts which have been mentioned, that very flight accidents may give the power of exciting contractions to a fingle metal, which had it not be fore; and that we may hence eafily account for the difcordant teftimonies of authors upon this point,

Hitherto I have spoken only of the effects of friction upon metals. But to conclude this part of my fubject, I must now remark, that charcoal, though from its friability not very fit for the experiment, may yet be rendered capable by the fame means of producing contractions, without the affiftance of any of the metals.

amination, greatly to exceed in number thofe of their agreement. When, therefore, two fubftances are known to have many properties in common, while their differences are few, and none of these abfolutely contradict fuch a conclufion, we infer with confiderable confidence, that they are the fame, though we may not be immediately able to explain why their refemblance is not complete. After Mr Walsh, for inftance, had discovered, that the influence of the torpedo was tranfmitted by all the various bodies which are good conductors of the electric fluid, philofophers made little hofitation in admitting them to be one and the fame fubftance, though fome of their apparent differences could not then be accounted for. In like manner, the inquirers into the nature of the influence, the effects of which are fo evident in Mr. Galvani's experiments, have very generally, and in my opinion juftly, allowed it to be electrical, on the ground that its conductors and thole of electricity are altogether the fame. To this, however, an objection has been made by Dr. Fowler, which, if well founded, would certainly prove them to be different fubftances; for he has afferted that charcoal, which is fo good a conductor of electricity, refufes to tranfmit the influence, upon which the motions in Mr. Galvani's experiments depend. In reply, I fall only fay, that Dr. Fowler muft have been unfortunate with refpect to the charcoal he employed; tince all the pieces I ever tried, and I have tried many, were found to conduct this influence.

trical or not.

The points of difference between any two fpecies of natural bodies, even thofe which, from the fimilarity of fome of their most obvious qualities have once been thought the fame, are found, upon accurate ex

Other arguments have likewife been urged against the identity of the two influences; all of which,

[*E 3]

how

however, excepting one, I fhall decline difcuffing, as they either are of little importance, or have not been flated with fufficient precifion. The objection I mean is, that in none of the experiments with animals, prepared after the manner of Mr. Galvani, are thofe appearances of attraction and repulfion to be obferved, which are held to be the tefts of the prefence of electricity. My anfwer to it is, that no fuch appearances can occur, in Mr. Galvani's experiments, confiftently with the known requifities for their fuccefs, and the established laws of electricity. For, as it has been proved, that there is naturally no difengaged electric fluid in the nerves and mufcles of animals, I except the torpedo and a few others, no figns of attraction and repulfion can be looked for in thofe fubftances, before the application of metals or charcoal; and after thefe have been applied, the equilibrium of the influence, agreeably to what has been already fewn, is never difturbed, unlefs means for its restoration be at the fame time afforded. Neither then ought figns of attraction and repulfion to be in this cafe prefented, on the fuppofition that the influence is electrical; fince it is neceflary for the exhibition of fuch appearances, that bodies, after becoming electrical, fhould remain fo during fome fenfible portion of time: at being well known, for example, that the paffage of the charge of a Leyden phial, from one of its furfaces to the other, does not effect the moft delicate electrometer, fufpended from a wire or other fubftance, which forms the communi, cation between them.

Such are the observations I mean at present to submit to the confider

HINKING that fome general

TH

deductions from the principal facts, or phenomena, mentioned in the courfe of this work may be expected of me, especially with refpect to the theory of the formation of the irregular furface of the earth, at leaft of that wonderful part of it which I have fo repeatedly explor ed, I have ventured to annex a for obfervations, which appear to me to merit the particular attention of philofophers, as likewife the con fequences which I think might be drawn from them.

I do not, however, mean to speak of what relates to the firft and great revolution experienced by our globe at the formation of its continents: that is, at the epoch when the wa ters covered it about two thousand four hundred and fifty toifes, and which is nearly the prefent eleva tion of fome of the granitic peaks of the Alps, as Mont Blanc, Mont Rofe, &c. In fhort, of the time when they were totally fubmerged by that element, and formed them felves under that fluid, either by effect of cryftallization or precipita tion. I therefore only intend ta touch on the phenomena which relate to the laft immersion experienc ed by our continent, and which appears to have been partial.

I. From the immenfe atterriffements, or land-accumulations, al ready formed, and which are con tinually increafing at the mouth of

the Pô; from the extreme variation or great variety exifting in the different ftrata of fand, pebbles, and vegetable earth, which now form the banks of that wonderful river; from the number of beds of maritime and fluviatiles, or river thells, which lie in fome places diftinét or feparated, and in others confufedly mixed together, from Cremona to the fea: in fine, from the progreffive diminution which the velocity of the waters of the Pò experience, in proportion as the lower valley of Lombardy enlarges and gets nearer the fea: I conclude or deduce the following confequences. 1. That that part of the valley, which lies eaftward of Cremoną, cannot owe its origin or inereale but to the quantities of earthy matter continually brought down and depofited by this river, which, to all appear ances, were formerly infinitely more confiderable than at prefent. 2. That the fea once covered this fertile plain; and that the greateft part of Lombardy may be confidered as an encroachment made on that element, by a quantity of fragments detached from the primordial and fecondary chain of mountains, which were at firft hurled by the fee in its laft retreat, and then carried along by the waters of the Po, which in fome degree till continues to depofit them, as before mentioned, by means of the frequent inundations caufed by the overflowings of the Po in the confines of Ferrara and Bologna, which are increafed by the eagernels of the inhabitants of thofe provinces, who unfortunately attempted to restrain the waters of that formidable river too foon by banks, dykes, &c.

II. From the direction of the valey of Lombardy, and of all the fe

condary ones which terminate in it; from the extreme difference in the elevation of the head of these secondary valleys fituated at the foot of the Alps, and likewife from their number, compared to thofe on the weft and fouth-weft of the fame mountains; from their irregular form, number, and great degree of abruptnefs, which exift likewife in the fecondary and tertiary mountains on the eaftern fide of the granitic peaks, in comparifon to thofe of the fame order on the weftern: in fhort, from the calcareous chain of hills which furround all Lombardy :. I think I may venture to conclude: 1. That the motion of the fea, in its first mutation or change, had a direction tending nearly from west to eaft. 2. That at first it rose to a great height, which appears to be fully proved by the calcareous mat ter, containing maritime fhells, now found lying on fome of the primitive rocks of the Alps. 3. That its motion and retreat, or fubfiding, were at firft extremely rapid. 4. That the feas having rofe above the plains which form the high valleys of the Alps, it afterwards precipitated itfelf towards the caft, and dug by its weight and ye locity the valleys which are at their feet, mutilating and chamfretting the fecondary mountains which intercepted its pallage. 5. That the fea, having in procefs of time abated in its mation, had by its fediment formed the fchiftus and fecondary mountains, which defcribe a kind of zone to the plain of Lombardy: in fhort, 6. That it is evident, that the fea remained or ftopped a much longer time on the western fide than on the eastern.

III. From the enormous maffes of granite and primitive rock which [* E 4]

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now lie isolated on the fummit of feveral high calcareous, fchiftous, and fandy-hills in Piedmont, to which they have not the leaft analogy, I am naturally led to believe, 1.That the foil of the upper part of the valley of Lombardy was, when fill covered or fubmerged by the fea, nearly as elevated as the fummit of thofe hills are at prefent. 2. That thefe granitic mafies were moft probably driven on the top of thofe hills by the accelerated action of the fea, as I have previously obferved in a former part of my work, and left in that ifolated state by the fame current, which, by gradually furrowing the foil in various directions, formed an innumerable quantity of fmall irregular valleys, which have, however, in general, their falient or prominent angles uniformly oppofed

to the concave ones.

IV. From the extreme degree of cold particularly experienced on the Cols de Tende, Finefire, and Argentera, c.. though lefs elevated than Mont Cenis, I draw the following conclufion, viz. That the height and degree of elevation of the mountains, above the level of the fea, have lefs influence than that which they have above their valleys, in order to the abfolute determination of the kind of climate which exifts on their fummit; provided, however, their height does not exceed one thoufand or twelve hundred toiles, that being nearly the zone in which the fnow is per

manent.

V. From the irregular inclinations or directions fo generally found in the beds or ftrata of the fecondary mountains, and from their abruptnefs, breaks, and quantity of heterogeneous matter fo frequently con

tained in their cavities, I am of opinion, 1. That those mountains could not have given way and funk, except at the time when their fummits were entirely fubmerged by the fea: indeed this fuppofition ap pears to be fully elucidated, by the calcareous matter containing marine foffils, which generally fill the va cuum formed by the different breaks of thofe mountains, and which is likewife fometimes found on their fummits. 2. That they could not have thus broken or separated, but from the effect of fubterraneous caverns formed in the interior of the

globe, the vaults of which, from being progreffively over-charged by a continual accumulation of cal careous particles depofited by the fea, have funk or given way, as, I Batter myself, I have in a former part of this work clearly demonftrated.

VI. From the number of mountains formed of grés, or fandftone, marne, or marl, and puddingftone, which lie on others of dif ferent fpecics, fuch as granite, rocktone, &c. which likewife vary as to the reciprocal inclinations of their trata; also, from the irrregularity and extreme verticality in the ftrata of the mountains of schift, which even form a right angle with the horizon; in fine, from the general diforder or confufion which appear fo confpicuous in the fecondary and tertiary mountains, fituated towar the weft and fouth-weft chain of the Alps, I am led to believe: 1. That the wonderful changes which our globe has experienced are entirely owing to the effects of fire and water, which have, at different epochs, powerfully and visibly acted either together or feparate. 2. That

the continents have likewife been expofed to fimilar revolutions; and, in fhort, that the last great débâcle, or bouleversement, is not, by feveral centuries, of fo remote a date as has been generally fuppofed.

VII. From the fandy hills which compofe the valley defcribed in the eighth chapter, containing different fpecies of marine foffils, and which are as if inclofed or wedged in the midft of high calcareous mountains, which do not contain any; from the direction of this valley, which tends from north to fouth from the petrified trees likewife found ten feet below the foil of the fame valley, in the environs of Nice, refting on calcareous beds, the roots of which contained in their ramifications a quantity of marine foffils; I am induced to conclude, 1. That the fea, in its flow and gradual retreat, must have formed an extenfive gulph in the neighbourhood of Efcarene; and that the calcareous mountains, above alluded to, ferved as its eastern and western boundary. 2. That the fummit of the fandy hills, which now form the inner valley, indicate as nearly as poffible the elevation of the bottom of the gulph at that period. In fine, that the waters having afterwards ef fected their retreat in that place, from north to fouth, had, as it were, traced out the valley, which has fince been finifhed by the draining of that part of the fea which had been accidentally retained in fome of the higher valleys, in confequence of having broken, by its weight and action, the calcareous barrier which for a time retained it. VIII. From the abrupt ftate of the calcareous mountains which border the Mediterranean coaft

from Nice to Savona; from their. extreme height or elevation; from the depth of the fea which washes their bafis; as likewise from the direction of the rivers and valleys of that part of the chain, which is in general from north to fouth, and the vaft number of gypfum quarries which are within a mile or two of the coaft; I am led to fuppose, 1. That the major part of the fecondary and tertiary chain of the Alps ftill remains covered by the fea. 2. That it appears probable that thofe mountains may extend to the islands of Corfica and Sardinia. In fine, that a number of these cal careous mountains owe their abruptnefs to the laft retreat of the fea, which had, by infenfibly undermining their bafis, occafioned part of their mafs to detach and fall into the water, from their not having at that period acquired the fame degree of confiftence which they now poffefs.

IX. From not having been able, with the greatest care and attention, to trace or discover the least indication of volcanic operations from La Bouchette, near Genoa, to Mont Vifo, in Piedmont, which are the two mountains which terminate the maritime chain, I think myself authorised to say that there does not appear to have exifted any volcanos in that part of the Alps, except in the valley of Fontaine du Temple, mentioned in the laft chapter, and which, from not having been able properly to investigate, I cannot to a certainty venture to give my opinion.

Thefe are the conclufions I deduce from the foregoing premifes and which I offer to the confidoration of the public with fome difli

denco