1880. ] Geography and Travels. 385 
Prof. John A. Church has recently written a book on “The 
Formation and History of the Comstock Lode.” His account 
of Comstock geology differs essentially from this. He concurs 
with his predecessors in regard to the position and order of the 
rocks and the presence of a dike under the lode; but he gives to 
the rocks and to the lode itself a different history. He finds that 
the diorite and propylite are both stratified, and their strata are 
approximately conformable. . 
ey were laid down in the horizontal position, and have been 
elevated into a mountain range by the ordinary operation of 
pressure and folding. The dikes of andesite have not broken 
through cracks opened across the other rocks, but are bedded, in- 
terposed between the strata of diorite and propylite. The open- 
ings between these strata were not originally so thick as the quartz 
seams now are. At first they were the merest partings between 
two layers of the propylite; and in accounting for the develop- 
ment of these insignificant crevices to ore-bodies two and three 
hundred feet thick, Mr. Church advances one of the most impor- 
when a number of them were involved in the process of substitu- 
tion, some would be completely removed, when others were only 
half dissolved away. If the process of substitution stopped at 
this stage, the result would be a mass of quartz inclosing streaks 
and layers of propylite, just as the structure is found to exist at 
the edges of the quartz bodies.—Engineering and Mining Fournal. 
GEOGRAPHY AND TRAVELS.’ 
! Edited by ELLIS H, YARNALL, Philadelphia. 
