BIOLOGICAL CHANGE IN GEOLOGICAL TIME. 109 



If this is so, and has been so, horizontally, time will make it so 

 vertically also, and this should give no cause before asserting 

 that a species has become extinct because it has not been found 

 so far in a bed above its so-called zone. It is indeed not too 

 much to say, that until all the fossiliferous rocks in all parts of 

 the world have been well examined, we ought not to positively 

 assert the restriction of a species to a particular zone or even to 

 a particular formation. 



Doubtless, extinctions in geological time have been in the 

 aggregate vast, but the time has been vast also. Some of the 

 extinctions, it is true, have embraced not only species but 

 genera, in a few cases families, and in a very few cases, only live 

 in all. Orders, but these have, in m.ost cases, if not in all, been 

 effected during long-extended periods of time. 



Causes of Biological Change. 



From the facts revealed by geology and palaeontology, a few 

 of which have here been very briefly presented, it is evident, I 

 think, that it will be most difficult to formulate a specific 

 cause, or specific causes, for specific biological changes, including 

 the appearance of new and the extinction of old forms. 



The hypothesis, which has been advanced, of natural causes 

 operating to effect a certain amount of change, or rather 

 modification, and these being supplemented by direct super- 

 natural action to complete the change and give a new species 

 or a new genus,* seems to leave out of sight the fact that some 

 newer species and newer genera were decidedly inferior to those 

 preceding them, for we can scarcely call in supernatural power 

 to reverse advance, to retard progress, and to undo good. The 

 more complex graptolites are from Lower Silurian formations 

 and the simpler forms from the Upper Silurian and Devonian 

 rocks. The largest and most highly developed genus of 

 trilobites, the Paradoxides, is in Lower Cambrian rocks, while 

 the two late Carboniferous genera, the Phillipsia and the 

 Griffithides, are both simple and small. The earliest Lamelli- 

 branchs were dimyarian and the much later Ostrea, Grypheo., 

 and others, were monomyarian. The tetrabranchiate cephalopods 

 flourished in Palaeozoic seas long before the appearance of the 

 dibranchiate genera. The Ammonite was not in advance of the 



* Dr. C. B. Warring, Journal of the Victoria Institute, vol. xxxvii, 

 p. 172. 



