GEOLOGY. 43 



mountains is lofty, it is not unusual to find the strata inclined 1'roni the 

 centre or axis of the chain towards either hand, and in such cases we 

 generally find the strata reposing on a different kind of rock, which has 

 no appearance of having a seamed or stratified structure. Hence the 

 two great divisions of stratified and unstrattfied. Sometimes mineral 

 bodies form irregular masses, entirely in the rocks in which they occur, 

 varying in weight from a few grains to many tons, without any 

 perceptible trace of the mode of their introduction. Occasionally long 

 fissures occur, which are not filled up by any solid material ; sometimes 

 also cavities are left in the more solid species of rocks, the sides of 

 which are lined with crystalline bodies, of various kinds. Sometimes 

 these fissures and cavities are of enormous extent, forming vast caverns 

 in the bowels of the earth, which are either empty, or filled with water. 

 Such is the general structure of the solid crust of our earth. But when 

 we examine the rocks more minutely, we find other striking peculiarities 

 belonging to each, which, besides the order of their superposition, mark 

 different eras in their formation. Minute examination of the organic 

 remains, collected from several strata, has established the fact, that 

 comparatively but few of the fossil animals are of the same species with 

 those of the same families now living, and we cannot doubt but that they 

 have wholly disappeared (genera and orders) from the face of the earth. 

 It is only in the upper deposits that any species, identical with those 

 now existing, have been detected. Y/here the organic bodies are 

 completely fossilized, very few, if any, living species can be recognized ; 

 and, generally, the recent species most nearly allied to the fossil are now 

 no longer to be found in the adjacent seas or regions. Thus the fossil 

 shells and corallines of northern countries, in both continents, have their 

 congeners (when such are known) generally in tropical climates, and the 

 fossil trees of the British coal fields have a greater affinity to the tree 

 ferns and cyacadecc of southern regions, than to any sort of European 

 vegetation. But it may be asked, how can Geologists fix so exact an 

 order of succession ? The answer to this is most complete, and they 

 come to the conclusion from unerring data. Every stratum contains, 

 within its own domain, records of its past history, written in characters 

 intelligible to all nations, which no possible events can falsify or destroy, 

 and which have enabled the Geologists to arrive at some conclusions, 

 possessing all the certainty of mathematical demonstration. The 

 following table will give a good general idea of the distribution of the 

 strata, as regards the United Kingdom. 



