112 Mr Charlesworth on the Age 



by a general estimate of the amount of resemblance borne to ex- 

 isting species, by the entire series of crag or London clay-fossils 

 taken collectively. This mode of procedure may, at first, offer 

 only a different adaptation of the numerical plan of Mr Lyell. It 

 will, however, be found an important modification of his princi- 

 ple ; for, when applied to the fossils of those formations, which, 

 from the presence of living species, can also be subjected to the 

 per-centage test, it will, under some circumstances, furnish re- 

 sults that clearly establish a fallacy in one of the two methods. 

 For instance, the red and coralline crag are supposed by Des- 

 hayes to contain the same number of extinct species ; and by 

 the per-centage test, they therefore present an equal approxi- 

 mation to the existing organization. But, if the shells, which 

 Deshayes thinks he can identify with those now inhabiting the 

 German Ocean, are rejected, and the extinct testacea alone com- 

 pared with living types, the forms most remote from existing 

 species will be found to occur in that series which has been de- 

 rived from the coralline crag. 



The author then changes his line of argument, and assuming 

 that there is a general agreement among conchologists, as to the 

 characters which should be depended upon in discriminating 

 species, and also that the per-centage test is the true method 

 of obtaining relations of analogy, he proceeds to inquire whe- 

 ther the association of organic remains in fossiliferous deposits 

 implies their previous contemporaneous existence ? The evi- 

 dence drawn from this source, appears to the author to be by no 

 means so conclusive as it has been generally considered ; and his 

 opinions have been formed principally from an attention to the 

 causes now in operation upon the earth^s surface. 



The small part of this island occupied by the crag formation, 

 is intersected, in one spot, with several estuaries, which have 

 completely removed this generally superficial fossiliferous stra- 

 tum, the bed of the estuary being formed in an older formation. 

 Along the banks of the Deben, which flows through a part of 

 the coralline crag, in some spots, the fossil shells line the shore in 

 greater numbers than the recent testacea ; and, during the period 

 in which this estuary has been formed, prodigious numbers of 

 these fossils must have been swept down into the German Ocean, 

 and there indiscriminately mingled with the reliquice of existing 



