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upon the docks at Erie, Pa. which he indentifies as fossil remains. 
Three plates follow the article. 
The Phosphate Deposits of Arkansas. By JOHN C. BRANNER, pp. 
580-598. The phosphate deposits are reported in or associated with a 
narrow zone either of greenish or black shale, or a sandstone deposited 
between recognized Lower Silurian and Carboniferous strata. This 
interval represents the slow accumulation of organic matter in acom- 
paratively deepsea. Phosphate nodules have also been found in some 
of the Cretaceous beds of the region. 
Magnetic Observation in Geological Mapping. By Hrnry Lioyp 
SMITH, pp. 640-709. ‘The principles of plotting magnetic observation 
and applications to geological mapping, etc. 
Some Mines of Rosita and Silver Cliff, Colorado. By S. F. EMMons, 
pp- 773-822. The ore of the Bassic mine was deposited by fumoralic 
action as a phase of the dying activity of the volcano when H,S and 
5,O were the prevailing gases. The Bull-Domingo mine ores were 
deposited from aqueous solutions coming from a region of igneous 
eruptions close at hand. 
Discussing the composition of descending surface waters and 
ascending deep waters Mr. Emmons concludes, in opposition to the 
prevalent belief, that decreasing temperature and pressure are not the 
principal determining causes of the precipitation of vein minerals from 
ascending solutions. Also that all the metallic minerals of the plateau 
were formed under the same conditions and during the same general 
phase of ore deposition, and their irregular dissemination is due to 
physical rather than to chemical causes. 
He states also that ‘‘the heavy metals have probably been brought up 
from the interior of the earth within the magmas of igneous rocks, and 
that by some process of differentiation not yet completely understood 
either previous to, or during the process of cooling and consolidation, 
they have been concentrated within certain bodies or parts of bodies 
of eruptive rocks ; and, further, that ore bodies as found at the present 
day are the result of a concentration (perhaps many times repeated) 
of the materials thus brought up, which are in all probability very 
finely disseminated through the present rock masses or combined in 
minute amounts in the more common basic minerals. This seems a 
more rational hypothesis, and one more in accordance with modern 
scientific practice, than to content oneself with assuming simply that 
