Reviews—Silliman’s American Journal. - 207 
spars with hornblende) of Canada;* noticing also instances of 
‘local metamorphism,’ and giving the results of the examination of 
specimens of a fossiliferous limestone altered by a doleritic dyke. 
Dr. H. Gispons describes the probable conditions of the springs 
near San Francisco, where, clay or other impervious rock underlying 
the superficial strata, the springs and streams reappear at the end 
of the dry season, as evaporation lessens with the decreasing heat of 
summer, before rain actually sets in. The New Almaden Quicksilver 
Mines are described by Prof. B. Silliman, jun. 
In the study of a particular seam of coal in Ohio, known as the 
‘Bear-Creek Coal,’ Prof. ANpREws finds much of interest in its 
laminated structure, which tells of alternating conditions of deposit, 
—in its contained pyritous and water-worn fragments of wood—and 
in its vertical planes of division, contemporary with the hardening 
the coal, and possibly determined, he thinks, by terrestrial elec- 
tricity. 
Prof. A. WINCHELL notes tne finding of the bones of a youngish 
Mastodon two feet under the surface of a small peat-bog in Michi- 
gan, and the probability of its having lived with the American 
Indian. The remains of Elephas Jacksoni, Deer, and Elk, accom- 
pany those of Mastodon in the bogs of Michigan. Dr. Scorr draws 
attention to the supposed change of level in a part of the Green 
Mountains. 
Californian Geology and Gold.—Prof. J. D. WuiItNeEy, giving an 
account of the progress of the Geological Survey of California, 
especially notices the great extent of fossiliferous Triassic rocks 
(St.-Cassian beds, &c.) in the Sierra Nevada, and probably in the 
Humboldt Ranges, and remarks that ‘a large portion of the auri- 
ferous rocks of California consist of metamorphic Triassic and 
Jurassic strata,’ that some are metamorphosed Cretaceous strata, 
and that no Paleozoic rocks have been there recognized. Creta- 
ceous rocks are wide-spread in California and Oregon, usually 
metamorphosed, but sometimes fossiliferous. The Tertiary beds 
of the coast-ranges are extensive and various; Mr. Gabb is at 
work on their fossils. The vast Tertiary formations on the flanks 
of the Sierra Nevada, which are dug and washed for gold, in the 
tunnel-mines and hydraulic works of California, are not of marine 
origin, nor spread out uniformly; but are formed of materials 
brought down from the mountain-heights in the later Pliocene 
period, under the action of causes similar to those now existing, 
but probably of greater intensity, and deposited in valleys, where 
they filled river-channels and lakes, and often imbedded whole forests, 
together with remains of land and fresh-water animals. 
These great detrital valley-deposits were covered over with vol- 
canic ashes, pumice, and lava-streams, issuing from the higher parts 
of the Sierra during a tremendous outbreak of igneous energy ; and 
since then, by the wear and tear of weather, the flanks of the Sierra 
* Both of these kinds of instructive anorthisites are alluded to in Dr. Bigsby’s 
paper on the Laurentian rocks in the Grotocican Macazine, No. III. 
