36 ANNUAL REPORT OF 



young Lepidosteus, long after it has been hatched, exhibits in the 

 form of its tail, characters thus far only known among the fossil 

 fishes of the Devonian system." * 



Still more suggestive was the same author's comment upon the 

 remarkable resemblance between the human fcetus in an early 

 embryonic stage and those of the shark and skate; the similarity 

 being so obvious that it may properly be claimed for higher ani- 

 mals, including man, that they pass through a "fish-stage," in 

 which even gills and a rudimentary tail are present during the 

 course of their early development. 



It is hoped that the above general observations will serve to 

 help the reader to a more or less definite idea concerning the scope 

 and aims of palaeontology, and the important influence exerted 

 by it upon other lines of inquiry. Coming now more par- 

 ticularly to the question of fossil fishes, it remains to sketch 

 in outline the general history of this class of vertebrates so far 

 as it is revealed to us by the palaeontological record, and finally to 

 discuss the relations of those fishes occurring in the Triassic rocks 

 of New Jersey to others that have preceded and followed them 

 during the course of geological time. First of all, it is necessary 

 to fix in our minds the chief divisions of the geological time 

 scale, in order that the chronological succession of fossil forms 

 may be kept clearly in view, and that we majr form a more ade- 

 quate appreciation of the time-interval between the Triassic fishes 

 of New Jersey, and the Palaeozoic, let us say, of adjoining States. 



Geological Time Scale. — Most persons are probably aware that 

 geologists divide the fossiliferous rocks into three principal series, 

 known respectively as Primary, Secondary and Tertiary, or more 

 familiarly as Palaeozoic, Mesozoic and Cenozoic — these latter 

 terms signifying "Ancient Life," "Mediaeval Life" and "Recent 

 Life." The term Archaean or Archaeozoic is applied to primitive 

 rocks of great thickness underlying the lowermost Palaeozoic, 

 none of which exhibit satisfactory evidence of organic life; if 

 they formerly contained fossils, these have become entirely oblit- 

 erated by metamorphic processes. The principal time-relations, 

 "eras" or "ages," as they are called, are subdivided into various 



1 Contributions to the Natural History of the United States of America, vol. 

 I. (1857), p. US- 



