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- l 
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 I 
in thickness, in which animal remains are rare. 
This slate is thinly laminated, and, according to the 
rules of geological interpretation, must have been j 
deposited at successive intervals in quiet waters. | 
III. 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 j 
of the two preceding periods, the strata bear evi- f 
dence of having been formed in waters alternately 
quiet and disturbed. Under these circumstances 
were deposited the whole series of this division, jj 
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, 
