1819.] Greenough on the First Principles of Geology. 461 



primitive formations ; though there can be no doubt that it is a 

 mere variety, or rather deviation, from another formation under 

 which it should he placed. 



The trap rocks in Germany are so imperfectly exposed that it 

 was very difficult in that country to form accurate conclusions 

 respecting their structure and position. This accounts for the 

 mistakes into which Werner seems to have fallen respecting 

 them. The same observation applies to the floetz rocks. Great 

 Britain is much better adapted for the study of these rocks than 

 Germany. In the middle districts of Scotland, the trap rocks 

 occur in vast abundance, and so fully exposed that they afford 

 the greatest facilities for examining their structure and position. 

 The same may be said of the coal formation which at Crossfell 

 and some other places is most admirably laid open for exami- 

 nation. 



It seems to be true that the primitive formations alternate with 

 each other differently in different places ; though several of the 

 examples brought forward by our author are, I believe, inaccu- 

 rate. The structure of the Grampians, for example, is repre- 

 sented as quite capricious ; yet, as far as I have examined it, 

 we find a great conformity, with the exception of those parts 

 where deposits of porphyry occur ; for this rock where it makes 

 its appearance, as at Glenco and in Cumberland, renders it very 

 difficult for us to make out the structure of the country. 



But there is a striking distinction between rocks which was 

 first pointed out by Lehman. Some rocks contain no traces of 

 animal or vegetable remains. We have, therefore, no evidence 

 that they have not existed since the original formation of the 

 globe. There are other rocks which contain these remains. 

 These must have been formed after the earth was inhabited by 

 animals and vegetables. They are not, therefore, original, but 

 secondary. They consist chiefly of fragments of the other rocks, 

 indicating that they were formed by the destruction of part of 

 these rocks, and that they involved with them the remains of 

 the animals and vegetables which at that time existed. Now it 

 is a matter of fact that the first of these rocks, or the primitive, 

 as they have been called, lie always (or almost always) below the 

 secondary, or have the beds of the secondary rocks reposing 

 against their sides. Here then is a regular arrangement of rocks, 

 clear, obvious, and undisputable. The primitive come first in 

 order, and they are succeeded by the secondary. 



It is true that one or two examples occur, as at Christiania, in 

 Norway, if Von Buch's observations be correct, where primitive 

 rocks are observed lying over secondary rocks, or rocks contain- 

 ing animal fossils. Such cases should be carefully described 

 and examined as exceptio?is to the general order of the arrange- 

 ment of rocks. When the degree of rarity of the occurrence of 

 such examples has been ascertained, and when all the phenomena 

 have been accurately examined, perhaps, it will be in our power 



