105 



species in foreign countries, but in North America it is 

 restricted to the base of the Lower Devonian group. 

 (Lower Helderberg and Oriskany beds.) 



Index species which have been successfully employed in 

 intercontinental correlation are Spirifer disjvnctus for the 

 upper, and Goniatites intumescens and Ithynchonella{Hypo- 

 thyris) cuboides for the lower, part of the Upper Devonian 

 group. 



While general correlation by index species is thus possi- 

 ble, much detailed work is necessary to establish the proper 

 relations between the beds occupied by these species at the 

 several localities. The nature of the sediment, and the 

 physical conditions indicated by it, and by the fossils them- 

 selves, must be taken into consideration, and the causes for, 

 and directions of, the migrations of the faunas must be 

 investigated. This method of investigation in correlative 

 geology is still in its infancy, and it requires for its proper 

 prosecution a thorough pahTeontological training. The 

 results to be obtained are certain to be of far-reaching im- 

 portance to both geologist and biologist. 



PALEONTOLOGY IN ITS RELATION TO BIOLOGY. 



(Paleobiology. ) 



The study of fossils, from a purely biological point of 

 view, has made such progress within the last fifty years, 

 and the results obtained have been of such importance, as 

 to raise palaeontology from a subordinate geological study 

 to the rank of an independent science. Not only have im- 

 portant discoveries in comparative anatomy, morphology, 

 and systematic zoology and botany been made by the study 

 of fossils, but it has become possible to trace out actual lines 

 of genetic descent in the organic realm. This has been 

 accomplished by the detailed study of particular classes of 

 organisms and the comparison of the several transient 

 stages in the life-history of the individual with the persistent 

 adult characteristics of those members of the same class 

 which preceded them in time. Such detailed study has been 



