246 BITUMINOUS COAL STRATA. 



and all to extinct species. These relics of a former 

 condition of our planet are so abundant, that the 

 conviction is forcibly impressed upon the traveller's 

 mind that he is treading upon the floor of an an- 

 cient ocean. Many ages must have elapsed, and a 

 peculiar condition of our planet prevailed, during 

 ^ the deposite of this vast mass of carbonate of lime, 

 as it is composed of numerous layers extending to 

 the depth of more than 600 feet, and contains 

 throughout its whole extent myriads of petrified 

 relics of animals, many of which must have lived 

 and died where we now find them entombed. 



II. In this division (marked C) there appears to 

 have been an important change, not only in the ma- 

 terials which were deposited, but in their organic 

 contents. 



Reposing upon the limestone already described, 

 occurs a body of argillaceous slate, 200 to 300 feet 

 ^ in thickness, in which animal remains are rare. 

 This slate is thinly laminated, and, according to the 

 rules of geological interpretation, must have been 

 deposited at successive intervals in quiet waters. 



ill. The rocks superimposed on the argillaceous 

 slate (D) appear to have been deposited under con- 

 ditions no less remarkable than the two preceding 

 divisions. Instead of the uniformly tranquil state 

 of the two preceding periods, the strata bear evi- 

 dence of having been formed in waters alternately 

 quiet and disturbed. Under these circumstances 

 were deposited the whole series of this division, 

 which consists of alternate layers of fine-grained 

 sandstone and slate, attaining a thickness of not 

 less than 300 feet. The layers of sandstone appear 

 to have been formed in a gradually shoaling bay, 

 estuary, or sea, for they are characterized by ripple 

 marks, which, it has been stated by Mr. Conrad, 

 can only be made in shallow water. These mark- 

 ings are sometimes so surprisingly regular and 

 beautiful as to appear artificial rather than natural, 



