150 Report of the State Geologist. 



special localities have been found where the appearance of new 

 forms have been carried forward. with a certain intensity. Thus 

 Hyatt*, after having studied thousands of individuals from the 

 principal deposits of Europe, decides that the cradles of the 

 various branches of the Arietidae are the basins of the C6te d'Or 

 and of Southern Germany. 



Transitions between genera and between the larger groups. — 

 The preceding remarks relating to the causes of the insuflB.ciency 

 of pal aeon tologic documents are applicable also to the terms of 

 transition which must have existed among the more extensive 

 groups, as genera, families, orders and classes. If the principle 

 of evolution is correct, forms the most isolated in appearance, the 

 most specialized types, must be connected by transition stages with 

 ancestral forms, whence other groups were derived. Palaeon- 

 tology brings to light a great number of these intermediate 

 types which have at the present day entirely disappeared. Thus 

 among the Echinoderms, the group of Cystidians embraces forms 

 which must have given rise to the types so well defined at the 

 present epoch, Asteroids, Echinoids and Crinoids. Among the 

 Vertebrates we recognize transitions between the Reptiles and 

 the Batrachians ; the most ancient of the Crocodilians, Lacer- 

 tilians, etc., differed less than do the living forms, and approach 

 nearer to the lowest type of the class, represented at present by 

 the genus Hatteria. The most ancient birds known had very 

 marked reptilian characteristics. Palaeobotany furnishes also 

 conclusive examples in plants ; the primitive forms of . the 

 Gymnosperms and Angiosperms are at present known. 



Palaeontology thus furnishes important arguments in support 

 of the continuity of animal or vegetable forms. IS'evertheless, 

 considerable gaps still exist. As in the case of species, these 

 gaps are gradually narrowed by the recent discoveries of exotic 

 beds. Thus, until the last few years, it was a matter of surprise 

 to see the Ammonites suddenly appear in the Trias, in forms 

 already very complicated, and with no apparent connection with 

 the Goniatites of the Carboniferous. But the recent investiga- 

 tions of Gemmellaro upon the fauna of Sicily, those of Waagen on 

 the fauna of India, have made known transition forms in the 



* Hyatt, Genesis of the Arietidce (Mem. 3Ius. Comp. Zool. Cambridge, 18S9.) 



