THE CANADIAN JOURNAL. 



NEW^ SERIES. 



No. LXXVII.— DECEMBER, 1872. 



THE IMPERFECTION OF THE PALtEONTOLO- 

 GICAL RECORD. 



BY H. ALLEYNE NICHOLSON, M.D., D.Sc, M.A., P.R.S.E., F.G.S., &c., 

 Professor of Natural History and Botany in University College, Toronto. 



As I have pointed out shortly in a former communication, the 

 series of the stratified formations is an incomplete one, and is likely 

 ever to remain so. The causes of this ''imperfection of the geological 

 record," as it has been termed by Darwin, are various ; but they are 

 chiefly to be ascribed to our as yet limited knowledge of the geology 

 of vast areas of the earth's surface, to denudation, and to the fact 

 that many of the missing groups are buried beneath other deposits, 

 whilst more than half of the superficies of the globe is hidden from 

 us by the waters of the sea. The imperfection of the geological record 

 necessarily imp^es an equal imperfection in the " palseontological 

 record j" but, in truth, the record of life is far more imperfect than 

 the mere physical series of deposits. The object, then, of this com- 

 rnvmication is briefly to consider some of the maia causes of the 

 numerous breaks and gaps in the palseontological record. 



I. Causes of the Absence of certain Animals in Fossiliferous 

 deposits : — In the first place, even if the series of stratified dej)osits 

 had been preserved to us in its entirety, and we could point to 

 sedimentary accumulations belonging to every period ia the earth's 

 history, there would still have been enormous gaps in the palseonto- 

 logical record, owing to the different facilities with which difierent 



