Ixxii PHOCEEDINGS OF THE GEOLOGICAL SOCIETY. 



Glohigerina in the cold area, while the extent of the other differences 

 loses much force by the identity of the Mollusca. We know not also 

 whether there is not a passage from one area to the other. We require 

 therefore more evidence before the geological value of the distinction 

 of the two areas can be fully accepted ; at the same time the impor- 

 tance and interest of such an influencing cause must be kept in view. 

 I will now say a few words on one of the most important bear- 

 ings that these deep-sea researches have on chronological geology. 

 Objections have been taken on various grounds to the percentage 

 test of Sir Charles Lyell, as evidence of relative age. The data of 

 the deep-sea dredgings furnish us with curious and apparently 

 paradoxical relults and such as might seem fatal to this test. Sup- 

 pose an isolated portion of the deep-sea Atlantic bed had been ele- 

 vated at some late period, and that we were yet ignorant, as we were 

 only twelve years since, of what was to be found in the unexplored 

 depths of the ocean. Suppose further that the Atlantic deposit had 

 taken place on such rocks as the Palaeozoic strata of Cornwall or 

 South Ireland. A chalky-looking deposit would then have been 

 found overlying old rocks, with nothing to indicate stratigraphi- 

 cally its geological position, and with fossils to a great extent new. 

 In the absence of a complete knowledge of the deep Atlantic fauna, 

 I will take, as a specimen of what they might have been, the result 

 of one deep dredging in 5964 feet. Mr. Jeffreys obtained in this 

 single dredging 186 species of Mollusca. Of these he found : — 



91 species recent or living. 



24 „ formerly known as fossil only, and belonging to the Plio- 

 cene strata of Sicily ; some of these are undescribed. 

 71 „ new or undescribed. 



18*6 

 The conclusion would have been that 95 out of the 186, or 51 per 

 cent., were of extinct species ; and of these, 24 would be referred to 

 Pliocene age. What would have been the inference as to the age of 

 the beds ? Certainly, on palseontological evidence alone, there could 

 have been but one conclusion. They must have been classed as 

 Pliocene or older, although these researches have now shown all the 

 species to be recent. 



The case, however, is an extreme and exceptional one. It is 

 true that, in future speculations, the possibility of such a case 

 happening must be taken into consideration ; but the depths of the 

 Atlantic are so great that, unless in case of a disturbance such as 

 that of the elevation of the Alps or the Andes, we are not likely 



