320 Dr. Mac Culloch on the Geology of Glen Tilt, 



that their death could not in all probability have long taken place. 

 As the animals themselves are known to be existing species, it is 

 indeed probable that this bed is still in a state of increase, however 

 tedious and imperceptible the process may be. 



Here then we have a fact which presents us with another 

 modiiication of those strata which owe their origin to the action 

 of living animals, or to the accumulation of their remains. It 

 has always been known that marine animals acted an essential 

 part in the production of the secondary, and even the latest of the 

 primary, (or transition^ strata. It has lately been shown that 

 considerabri2 deposits and large beds of rock have also in former 

 -times been produced by testacea inhabiting fresh waters. But 

 it has never been suspected that timilar deposits could be formed 

 on dry land. That such is the case here, is sufficiently evident 

 from the angle of acclivity on which this bed is formed, on a 

 surface which has assuredly undergone no alteration of its position 

 since its formation, or at least since the formation of the granite. 

 The fact itself is much too insulated and too narrow to admit of 

 :any generalization, or to justify us in supposing that similar for- 

 mations might have taken place in a more ancient state of the 

 globe. Else speculative minds might conceive that of the nume- 

 rous elevated and apparently displaced strata which are now fcimd 

 <;ontaining organic remains, of which, not only the species, but the 

 very genera as well as habits are unknown, some at least might 

 have been deriv,ed from land animals, whose remains were converted 

 into rocks in the very places where they now exist. Should causes 

 ^with which we seem but very imperfectly acquainted at present, 

 hereafter convert the marie bed now described into a rock, and all 

 traces of its recent formation disappear, a circumstance at least 

 within tke limit of possibility, assuredly future geologists would 



