THE TRIASSIC PERIOD. 29 



that considerable changes in the physical geography of the northern 

 Pacific were in progress during the period. In the early Trias, the 

 waters of the Pacific coast seem to have been in such connection with 

 those of the Indian and Arctic oceans that animal life was able to 

 migrate back and forth 1 between these various regions, and the tem- 

 perature seems to have allowed much wider migrations in latitude 

 than are now common. In the Middle and Upper Trias there seems 

 to have been faunal connection with the Mediterranean region, per- 

 haps by way of the Indian Ocean. 



Climatic Conditions. 



The character of the conglomerates in some parts of the Triassic 

 system has been made the basis of an argument for a cold climate 

 during the Triassic period; but although the coarseness and litho- 

 logic character of the conglomerate are quite sufficient to suggest 

 glaciation, they do not prove it, and the few fossils found do not bear 

 out the suggestion. 



Some of the peculiarities of the conglomerate might be explained 

 if the climate were arid. In such climates, the expansion and con- 

 traction due to changes of temperature are so great as to be very effec- 

 tive in disrupting rock if its surface is not covered by soil or other 

 debris. Under such circumstances, much coarse debris originates, 

 largely of rock which is undecomposed. Violent storms (cloudbursts), 

 which often characterize arid climates, might account for the trans- 

 portation of debris from the place of its origin to the place of its depo- 

 sition. For the formation of abundant debris in this way, steep slopes 

 are needful, for gentle slopes and flats soon get a covering of soil or 

 mantle rock which prevents the disruption of the rock beneath. If 

 this were the origin of the coarse materials of the conglomerate, their 

 rounding and wear would have to be attributed to the waves of the 

 body of water in which deposition took place. The wide distribu- 

 tion of gypsum and salt in the Triassic system, not only of America 

 but of Europe, is a positive argument for wide-spread aridity. 



Close of the Trias. 



Considerable geographic changes marked the close of the Triassic 

 period in eastern North America, especially to the north, bringing 



1 Smith, Jour. Geol., Vol. Ill, p. 375. 



