Related Geological Conditions 43 



origin in Utah, often 30 - 50 ft. thick, says that "some 

 of these deposits are interbedded with lacustrine sediments 

 of Tertiary age," while those of Washington and Oregon 

 "contain the leaves of Tertiary plants, or are associated 

 with lacustral sediments and lava flows in such a manner 

 as to show that they are of Tertiary age." And again he 

 says: "The volcanic dust of the Pacific States sometimes 

 contains the bones of mammals, and is frequently charged 

 with quantities of leaves, showing that some of the tempests 

 generated by volcanic agencies were disastrous to animal 

 and plant life. These and related disturbances in environ- 

 ment probably had much to do with the modification and 

 extinction, especially of the higher mammalian species." 



An equally interesting phase of the subject is given by 

 the same geologist, who describes Lake Mono, "a body of 

 intensely alkaline water" at the base of the eastern slope 

 of the Sierra Nevada. In rowing over to two islands that 

 rise in it he says: "The water over which we pass gives 

 the fingers a slippery feeling; if we taste it we find that it 

 is intensely alkaline and bitter. As we look down into the 

 water we see that it is clear and limpid, but the view is 

 usually obstructed by countless numbers of brine shrimps 

 {Artemia) and larvae of flies. The larvae are thrown 

 ashore by the waves in windrows that are frequently a foot 

 or more deep." We might add to the above that were such 

 to be suddenly covered by a volcanic layer of dust, this on 

 hardening would present exactly the type of rock, and the 

 group of organisms, that Rupert Jones repeatedly refers 

 to in his monograph on the Phyllopoda. 



The celebrated eruption of Krakatoa in 1883 was so 

 carefully noted by many observers, and the results were so 

 accurately correlated and recorded by Verbeek (20) ; 

 and by the special committee of the Royal Society {21; 

 passim), that many lessons of great value in the present 

 inquiry can be gathered. 



As to the origin of the enormous amount of dust ejected, 

 and which in varying grades of fineness spread over the 

 atmosphere of nearly the whole world, Judd gives a graphic 

 description thus: "the great bulk of the volcanic dust of 

 Krakatoa was undoubtedly formed by the striking together 



