THE TRIASSIC PERIOD. 49 



It has been noted that the sea during the Permian period withdrew 

 from the northwestern portions of Europe, but lingered in the south 

 about the Mediterranean, and in the east in Russia. At the climax 

 of the retreat, the sea seems to have been confined more narrowly to 

 the Mediterranean region. In Asia, the sea had lingered in Turkestan 

 and northwestern India (Salt Range and Himalayas). In the latter 

 region the sea seems even to have advanced, for there is an uncon- 

 formity below the Permian, and, by retaining the ground thus acquired 

 till after the opening of Mesozoic time, afforded a theater for the great 

 transition from the Paleozoic to the Mesozoic. It is inferred from 

 the appearance of a specialized marine fauna in Siberia early in the 

 Triassic period, that the sea lingered on the continental platform some- 

 where in that quarter through the Permian and into the Mesozoic, and 

 that this also was an originating tract of faunas. These three regions, 

 the Mediterranean, the Himalayan and the Siberian, are the best known 

 tracts into which the shallow-water marine life of the Paleozoic retreated 

 and underwent transformation into the early provincial faunas of the 

 Mesozoic. It is quite certain that there was at least one other area 

 where important fauna! reorganization took place, for a notable fauna 

 suddenly appeared in the Middle Triassic, which does not seem to 

 have originated in any of these three districts. Very likely there were 

 still others. 



The transition faunas. — In each of these areas an important rem- 

 nant of Paleozoic sea life seems to have persisted and to have under- 

 gone a radical and perhaps rather rapid evolution, such as might be 

 anticipated from the crowding of the great faunas of the Carboni- 

 ferous times into such limited areas, relieved only by the narrow coast- 

 border tracts and incidental dependencies. From these areas the 

 new faunas spread forth as the sea again extended itself upon the 

 land. 



In the Indian basin there is a nearly continuous record of the transi- 

 tion from Paleozoic to Mesozoic marine life. Beds containing the 

 characteristic life of the Permian, the Productus fauna, are immediately 

 and conformably followed by beds containing the ammonite Otoceras, 

 and other forms of characteristic Mesozoic life. In the Productus 

 beds below the dividing horizon there are forms foreshadowing the 

 Mesozoic types, and in the beds above that horizon there are forms 

 of the Permian type that lived on past the dividing datum, and com- 



