silver adheres at the moment of precipitation to the surface of the copper, where it forms a kind of moss. In proportion as the silver is precipitated, the water assumes a blue tinge; which proves that the copper is dissolved in the nitric acid, in the room of the silver. When the whole of the silver is disengaged, and the water is poured off, the silver is dried, and fused in crucibles, to be cast into ingots. This silver, however, almost always retains a small quantity of the copper. Silver is likewise precipitated by mercury, and as the arrangement gives the form of a vegetation, it is called arbor diana. There is also a powder, lately discovered, to be produced from silver, more astonishingly fulminating than even fulminating gold itself. Gold is precipitated from its solution by several metals, such as lead, iron, silver, copper, bismuth, mercury, zinc and tin. This last precipitates it instantly in the form of a powder. Gold may likewise be precipitated from its solution by æther. This liquor seizes the gold in a moment, and sometimes instantly revivifies it. The gold is sometimes seen to form a stratum at the surface of the liquor, and the two fluids no longer to contain a particle. Copper ore, sometimes forms sulphate

* Berthollet.

of

1

of copper in its decomposition. This salt is dissolved in water, and forms springs more or less loaded with it, from which the copper may be obtained by cementation. Old iron is thrown into the water, the copper is precipitated, and the iron takes its place; not that the iron, according to vulgar belief, is transmuted into copper. In this manner it is obtained in Hungary, in England, and in Ireland. The skeletons of animals are sometimes found in copper mines, penetrated with that metal. We read even of a human carcase found in the great copper mine at Fahlun, in Sweden, which had remained there forty years, with the flesh and bones entire, without corruption, and without emitting any smell.*

* Acta Literaria Suec; anno 1772.

Hh3

LETTER

LETTER XXXI.

THE science of fossils comprehends, as you have seen, the knowledge of all the various bodies which are dug from the subterraneous parts of the earth; whether they be such as were naturally formed there, or originally belonged to the animal and vegetable kingdoms, and were deposited by some change in the course of nature. The Heathens adopted the most whimsical notions of fossils. They could not account for them. Even Pliny and Theophrastus believed (or seemed to believe), that stones bred, and brought forth young ones.* Nor is the mist even yet dispelled, for as I have already remarked, it has been a question with philosophers, whether stones do not grow in the earth? There certainly, however, seems to be no clear evidence to prove, that an integral pebble buried in the earth, is larger now than it was a thousand years ago. The contrary, indeed, is plain, from its retaining those marks of attrition which pebbles get by rolling against each

* Philosophy of the Elements.

each other in the water. Thus much, however, does appear, that there is in some parts of the earth a petrifying fluid, with which a broken stone will be reconsolidated like a broken limb; and heterogeneous matters, as shells and pebbles, will be found coagulated into a strong mass.

But let us cast our eyes again on the great subject on which we were engaged, and from which we have strayed, merely from the desire of running through the whole system of crystalization. Again let us plunge into the body of the waters. The continents on which we stand, were, as we have formerly said, the bottom of the sea. The surface which we now behold, received its configuration from the currents, the movements, and the inexplicable accidents it met with in the ocean. In the internal parts of the earth, as far as the excavations made by natural causes or by the industry of man, have given scope for observation, we have had striking marks exhibited, of the immense changes that have been produced by the chymical action of bodies on each other, during a course of ages preceding all human record. The loftiest mountains, which run in chains through the great continents, and are composed chiefly of granite, were found, previously to the existence of animals

and vegetables upon the present earth. The same also, it is presumed, applies to mountains of lime stone, or marble of a granular texture, and is grounded on the consideration, that the remains of organized substances are never found in them.* Calcareous stones, says De Saussure, are universally allowed to be productions of the sea. To prove this, the vestiges of marine animals may be demanded. be demanded. But the sea does not in every part of it produce shells. Moreover, there are oftentimes local causes, such as an abundance of the acid principle, which may alter and hinder petrification, nay even preservation. I have observed, continues this philosopher, and with great astonishment, in the argillaceous hills of Tuscany, and above all, in the environs of Sienna, for instance, near Monte Chiaro, that the hills contiguous to each other, are many of them so filled with fossil shells, that the earth has absolutely been white; but, on the contrary, that the others have been without the smallest trace of a shell. In the high mountains of the Alps, the slates, and calcareous stones, which appear to have been formed immediately after the primitive rocks, seldom or never contain vestiges of marine animals; whereas those in the flat country,

Nicholson's Philosophy.

or