70 



ON GEOLOGY. 



VEINS, as if the rocks they compose had split asunder in different places from 

 top to bottom, and the chasms had been afterward filled up from other 

 sources. These transverse lines or veins are worthy of notice in regard to 

 their shape and the substances with which they are filled. 



With respect to their shape, they appear to be almost always widest above, 

 and gradually to diminish as they deepen, till at last they terminate in a 

 point; exactly as if they had been originally fissures in the rock. Occa- 

 sionally, indeed, they are observed to widen and contract alternately in dif- 

 ferent parts of their course ; but this is by no means a common appearance. 



Sometimes they are partially or altogether empty ; and in this case they 

 are real fissures, and are so denominated; but generally they are filled with 

 matter more or less simple, and more or less different from the rock 

 through which they pass. All the formations I have already noticed as 

 existing in the shape of rocks have also been found in the shape of veins : 

 whence we have veins of granite, porphyry, limestone, basalt, wacke, green- 

 stone, quartz, clay, felspar, pit-coal, common salt, and metals of every kind. 

 When the veins are compound, or consist of a variety of substances, these 

 substances are almost always disposed in regular layers ; one species of 

 mineral constituting a central line or cylinder, and this being incrusted with 

 a second mineral, and the second with a third, and in the same manner to 

 the utmost sides of the veins. These layers are occasionally ver)'" numerous ; 

 that of the vein Georgius, at Freyburg, consists of not less than nine, and 

 there is another in the same district, which, according to M. Werner extends 

 to thirteen. It is not uncommon to find veins crossing each other in the same 

 rock ; and when this occurs, one of the veins may be traced passing through 

 the other without any interruption, and com.pletely cutting it in two, the cu 

 vein always separating and vanishing at the point of intersection. 



Nothing appears more obvious than that these veins must have been origi- 

 nally fissures produced by some unknown violence in the rocks in which they 

 occur; and it is highly probable, as conjectured by.M. Werner, that the mine- 

 ral materials which constitute them have been deposited slowly from above 

 during the formation of the different classes or sets of rock of which the dif- 

 ferent layers consist, while the rocks in which they occur were covered with 

 water. Upon this theory veins are of course newer than the rocks in which 

 they are met with, and which must have split to have produced them: and 

 where two veins cross each other, that is obviously the newest that traverses 

 the adjoining without interruption, as the fissures constituting the second vein 

 must have been formed after the first was filled up. 



The FIVE classes of rock formations we have thus far considered are those 

 which entered into Professor Werner's system, as it first made its appearance. 

 They are supposed to exist over the globe generally, and to be independent 

 of chorographic or typographic changes, and have hence been still farther 

 denominated universal formations. 



M. Werner has since, however, been induced to add to these a sixth class, 

 consisting of what he has called partial or local formations : comprising 

 those which are so often found in vast hollows or basins of particular coun- 

 tries ; the materials of which are, in many instances, strangely intermixed, 

 and have probably been carried down into such basins by circumscribed 

 deluges, produced by an exundation of rivers or seas, occasionally alter- 

 nating with each other, or by other partial disruptions. We have here, there- 

 fore, reason to expect, — what in fact is perpetually met with,— a motley 

 combination of whatever substances may have existed in the course of such 

 seas or rivers or rifted soils, with masses or fragments of most of the univer- 

 sal formations, alternate beds of marine, and fres?i water alluvions, and, 

 consequently, animal and vegetable remains of all kinds. 



The composite rocks that fill up the great basin around Paris, in which the 

 skeletons of so many unknown animals, even quadrupeds of the hugest size, 

 elephants, hippopotami, tapirs, mammoths, and other pachydermatous, or 

 thick-skinned monsters, have been discovered, are of this local formation. 

 The celebrated quarries of ^Eningen, on the Rhine, are of a like kind ; and 



