Review of Recent Geological Literature. 385 
and in the spongy nature of the gold. But the general 
structure and the presence of very rich sulphide ore con- 
taining antimony, arsenic, tellurium and copper are all indi- 
cative of the existence of rich ore, probably in very irregular 
deposits, but that may be followed to a considerable depth. 
In other words, the ore is not all superficial and secondary. 
There will certainly be found ore shoots extending down- 
ward for many hundred feet. 
The expense of prospecting such irregular lodes and 
the cost of mining and treating such complex ore in treach- 
erous ground lead to the conclusion that low grade ore 
will never have a value in Goldfield ; but that the assay 
value must be from fifteen to twenty dollars per ton to 
furnish any profit. 
My opinion on the whole is very favorable ; and I look 
to see a large production of gold for many years to come 
from the Goldfield district. h. v. \v, 
• Butte, Montana, May 15, 1905. 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Effect uf Cliff Erosion on form of Contact Surfaces. By N. M Fen- 
NEMAN (Bulletin Geol. Soc. Amer., vol. 16, pp. 205-214.) 
This is a suggestive paper in a somewhat new field of observa- 
tion and theory. The problem was encountered in an investigation 
by Mr. Fenneman, of the contact relations of the Wyoming Red 
beds with the underlying granite of the Front range of the Rocky 
mountains. The field of study was the southern half of the Boulder 
and the northern part of the Denver quadrangles. 
In this area the sandstones were evidently laid down on a sub- 
marine land surface of considerable relief, but the details of the 
relief were quite unlike the forms produced by stream erosion and 
the granite at the contact surface is as free from the products of 
weathering as the rock many feet below the contact. 
Mr. Fenneman points out that the surface of contact between 
unconformable formations will, of course, have some dependence 
upon the topography of the preexisting land surface. The surface 
of contact is visible only in section; if this section is a straight line, 
the surface is presumably a plane. The more the line deviates from 
straightness, folding aside, the more rugged is the topography- 
which may be inferred. 
