i88i. 



55 



Trans. N. V. Ac. Set. 



at Eureka, Nevada, where houses and cellars are excavated in the soft 

 material which forms the sides of the valley ; at Challis, in the banks 

 of Salmon River and Garden Creek, whence the specimens described 

 by Mr. Julien came, and in the caiions of the Des Chutes and its 

 tributaries in Oregon. 



Economically these rocks have considerable importance, as they are 

 extensively used in place of fire-brick for lining lead-smelting furnaces, 

 being very refractory, and easily dressed into shape with an old axe. 



Aj cs V_\vvt.\.e& . v\'vvt.T 





/■( I M I I I I I I I I 



II 1 1 n 1 1 1 I M !.ii 



11 LI J M \_\ 11 rr 



"I in 1 1 I I M n II I I'll 



^9/V//////J///////J/////>^A 





/ifrrrm 1 1 j 1 1 nrrn n \ m m i h i 

 fi fn il iTi M n ifiTFn ifi iTi n I Ti il 1 1 



nrri i ij 1 1 1 1 n 1 1 1 1 1 1 1 i n 1 1 1 1 r 



^ 



/iTi II I I I I ■ 1 I I I I I I I I I I I I 1 I 1 I t I I I I I I I 1 



i' 



6. 



7 

 i- 

 f 



I! 



a 



i2 



/¥ 

 li- 



/(, 



n 



a 

 II 



:lo 



21 



The above section represents the filling of some of the fresh water lakes which formerly 

 existed in Oregon just east of the great volcanic cones of the Cascade Mountains. Numbers 

 I and n represent sheets of basalt, the even numoers softer tuffs and bed of diatomaceous 

 earth, the odd numbers consolidated conglomerates of volcanic materials called "concrete" 

 in my notes. 



The study of a large number of outcrops of this series of rocks from 

 Southern Arizona to the Columbia River, has convinced me that they 

 are generally volcanic ashes which have been washed down and more 

 or less perfectly stratified in bodies of water which formerly occupied 

 the intervals between the mountain ranges of the great basin. On the 

 Des Chutes a section of more than looo feet shows 25 alternations of 

 strata, many of which are examples of the rocks in question. Here they 

 are interstratified with beds of tripoli, composed of fresh-water 

 diatoms, and layers of basalt. Some of the ash beds are almost entirely 



