1881. D5 Trans. N. Y. Ac. Sez. 
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 carions 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. 
Ee 
UTAUICAUARERAEHSRERUE Too ee 
eee ee et Sk Te 
iO SSon Se Se a Se Se oS SS ee eee 
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 
x and rz represent sheets of basalt, the even numbers 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 trom 
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 1000 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 
