ABSTRACT OF MONOGRAPH. 3 



tai'ies of Lake Lahoutan. The existing lakes are next considered. These 

 are Honey Lake, CaUfornia ; Pyramid, Winnemucca, Humboldt, North Car- 

 son, South Carson, and Walker lakes, Nevada. Each of these is described 

 with some detail with special reference to its geological bearings. All 

 the lakes mentioned above, excepting Humboldt, are inclosed, t. e,, are 

 withoiit outlet, and their waters stre somewhat saline and alkaline, but not 

 concentrated brines. They cannot, therefore, be considered as remnants 

 left by the incomplete desiccation of Lake Lahontan. The Soda lakes, 

 near Ragtown, Nevada, are specially considered, and detailed observa- 

 tions are presented which show that they occupy extinct volcanic craters 

 (page 73). Attention is given, on page 81, to the peculiar playas or broad 

 mud-plains of the arid region of the Far West, as well as to the temporary 

 lakes, called playa-lakes, which frequently flood them. 



Chapter IV (on the physical history of Lake Lahontan) is divided into 

 sections. 



Section 1 contains a compendious discussion of shore phenomena in 

 general. 



Section 2 is devoted to the presentation of the shore phenomena of 

 Lake Lahontan, and contains detailed descriptions and maps of the terraces, 

 bars, embankments, etc., that were formed about its shores. The highest 

 of the ancient water lines is named the "Lahontan Beach." It indicates the 

 maximum extent of the lake as shown on the accompanying pocket map. 

 The most conspicuous terraces below the Lahontan Beach are the "Lithoid", 

 "Dendritic", and "Thinolitic." Each of these marks the upper limit of a 

 variety of tufa from which it derives its name (page 102). 



Section 3 treats of the sediments of the lake and presents detailed sec- 

 tions of the exposures observed. The sediments consist of two deposits of 

 lacustral marls, separated by a heavy layer of current-bedded gravels; thus 

 recording two lake periods and an intermediate low-water stage (page 43). 



Accumulations of pumiceous dust, white marl, and aeolian sands are 

 described under the head of Exceptional Sedimentary Deposits (page 146). 



Section 5 is devoted to the illustration of geological structure, as dis- 

 played in the lake basin, and is followed by a rdsumd of the physical 

 history of the lake (page 169). 



