142 TOWN GEOLOGY. [vi. 



against each other still more, as those of our mountains 

 have been. 



But here may arise, in some of my readers' minds, 

 a reasonable question If these upheaved beds were 

 once horizontal, should we not be likely to find them, 

 in some places, horizontal still ? 



A reasonable question, and one which admits of a 

 full answer. 



They know, of course, that there has been a 

 gradual, but steady, change in the animals of this 

 planet; and that the relative age of beds can, on 

 the strength of that known change, be determined 

 generally by the fossils, usually shells, peculiar to 

 them : so that if we find the same fashion of shells, 

 and still more the same species of shells, in two 

 beds in different quarters of the world, then we 

 have a right to say These beds were laid down at 

 least about the same time. That is a general rule 

 among all geologists, and not to be gainsaid. 



Now I think I may say, that, granting that we can 

 recognise a bed by its fossils, there are few or no beds 

 which are found in one place upheaved, broken, and 

 altered by heat, which are not found in some other 

 place still horizontal, unbroken, unaltered, and more 

 or less as they were at first. 



From the most recent beds ; from the upheaved 

 coral-rocks of the West Indies, and the upheaved and 

 faulted boulder clay and chalk of the Isle of Moen in 

 Denmark downwards through all the strata, down to 

 that very ancient one in which the best slates are found, 

 this rule, I believe, stands true. 



It stands true, certainly, of the ancient Silurian 

 rocks of Wales, Cumberland, Ireland, and Scotland. 



