COLOR OF LACUSTEAL SEDIMENTS. 169 



muddy surfaces are pitted by falling rain-drops or covered with ripple marks. 

 When the waters again cover such an area, all these records may be concealed 

 beneath superimposed strata and thus preserved for an indefinite time. 

 They are, in fact, as well suited to become fossilized as the records of a 

 similar nature so common among the Triassic rocks of the Atlantic slope. 

 The markings inscribed on the surfaces of lake beds are identical with many 

 records that are made on the sands and mud along the ocean's shore, and if 

 fossilized, would in themselves give no indication of the character of the 

 water-body on the borders of which they were formed. 



COLOR OF LACUSTRAL SEDIMEKTS. 



From the study of the Triassic, Old Red Sandstone, and other forma- 

 tions of Europe,*^ Professor Ramsay was led to the conclusion that sedi- 

 ments deposited in inland waters were usually iron-stained. The reverse 

 of this conclusion would probably have been reached had lake deposits 

 been first studied in the Great Basin, as all the lacustral beds in that region 

 are light colored and seldom show more than a trace of the presence of iron. 

 Some of the inclined beds in the Walker River section have a pink tinge, 

 due to the pi-esence of iron, while some of the contorted sands we have 

 described have a yellowish color. These features, however, are inconspic- 

 uous and do not affect the statement that the sediment in question are a 

 total exception to the rule referred to above. 



RESUME OF PHYSICAL HISTORY. 



To arrive at a satisfactory understanding of the ph3'sical history of 

 Lake Lahontan, as recorded in terraces, gravel embankments, deltas, sedi- 

 mentary deposits, river channels, etc., it is necessary to combine our obser- 

 vations of these phenomena with the records of the chemical history of 

 the lake as furnished by tufa deposits and desiccation products, with refer- 

 ence, also, to the present physiography of the basin. Before considering the 



°^"0n the Physical Kelations of the New Red Marls, etc.," Quarterly Journal of the Geological 

 Society of London, Vol. XXVII, p. 189. Als .: "On the Red Rocks of England of older date than the 

 Trias."i&id.,p.241. 



