BOOKS AND CURRENT LITERATURE 15 



His chapter describes the general surface features of the country, and 

 discusses its exploration and early mapping. It forms the natural 

 introduction, and would have been placed first except for the desire 

 to pay a graceful tribute to Professor Blake's pioneer explorations. 

 The next chapter, by Mr. Free, goes further into the question of the 

 origin of the ancient lake and the general character of the basin. A 

 series of Tertiary strata, now uplifted and folded, lies at the foot of 

 the surrounding mountains. This formation is clearly of subaerial 

 origin, a piedmont deposit washed down from the highlands under 

 conditions of aridity. It indicates that for a long time during the 

 Tertiary era the basin was not occupied by the sea, and was essentially 

 like the other basins of the Southwest. In far more recent times, that 

 is within the last few thousand years, the basin has also been free 

 from the sea, for innumerable shells show that it was pccupied by 

 fresh water. Moreover, the strands of Blake Sea, which may date 

 back no more than 500 years indicate a very brief stand of the lake 

 at the level of overflow. If an arm of the sea were cut off, the water 

 must have stood at an approximately uniform level for many centuries 

 while the delta was being formed, and there ought to be a pronounced 

 bench in the rock, but none is found. Hence Free suggests that the 

 whole region may have been above sea level for a long period. At 

 first it was a simple trough. This was gradually depressed, but the 

 delta of the Colorado was built up as fast as the. land sank and a genuine 

 basin was thus formed in its rear. This was occupied by water only 

 when the Colorado temporarily shifted its course. Aside from excep- 

 tional periods of this sort, the Salton region appears to have had a 

 history like that of the typical desert basin. Free's interpretation 

 needs further study, but it seems likely to prevail. 



The relation of the Salton tufas to organic life suggests that the 

 chemical deposits of interior basins can be understood only by a study 

 of the effect of different types of bacteria or algae upon chemical reac- 

 tions. Papers by Ross and Vinson give details as to the concentra- 

 tion and composition of the water of the Salton Sea at frequent inter- 

 vals since the last inundation. Pierce follows with an interesting ac- 

 count of micro-organisms in highly concentrated brines. He shows 

 that living algae are found in water of a surprisingly high degree of 

 salinity, and that their activity varies in harmony with changes in the 

 degree of concentration. Brannon considers another phase of the same 

 matter. He immersed pieces of wood in Salton water for long periods. 

 When the water was sterilized, little decortication took place. Chemi- 



