114 
PALEONTOLOGY: C. A. DAVIS 
The relation of dikes to schist layers, the fact that lit-par-lit injection 
tends to neutralize chemical and physical differences between the 
magma and the invaded rock, the probable low temperature of the gran- 
ite, and the fact that positive evidence of absorption or assimilation on a 
large scale is lacking, all support the beHef that physical displacement 
and not assimilation was the primary process by which the forward 
movement of the magma was accomplished. The possibility that large 
blocks of roof in the areas of harder quartzite have been engulfed in the 
magma, and that this process was in these areas an important one, must 
remain an open question. In the main it is considered that the magma 
actually displaced the rocks either along great rifts or by pushing the 
yielding softer rocks before it into recumbent folds. 
ON THE FOSSIL ALGAE OF THE PETROLEUM- YIELDING 
SHALES OF THE GREEN RIVER FORMATION OF 
COLORADO AND UTAH 
By Charles A. Davis 
BUREAU OF MINES. WASHINGTON. D. C. 
Received by the Academy, January 2l, 1916 
In the region extending from northwestern Colorado west into Utah 
and north into Wyoming, there are great areas of, generally, carbonace- 
ous shales, which, in places, exceed 3000 feet in thickness. Scientific, 
as well as economic interest has been aroused in these shales, because 
they have recently been discovered to yield petroleum when subjected 
to destructive distillation in closed retorts. These shales are typically 
dark brown in color, very fine grained, hard, firm, tough and compact, 
except where weathered into thin, more or less curled and brittle laminae. 
Surfaces long exposed to the action of the weather bleach to whitish or 
yellowish gray. Some beds in the series of these shales already examined 
are so highly carbonaceous that they closely resemble compact lignite 
in appearance and burn readily when heated; other beds contain rather 
high percentages of finely divided mineral matter. 
When freshly broken, the rock gives off a distinctly bituminous odor, 
but, so far as observed, it contains no free oily compounds, although 
nodules and particles of a substance resembling asphaltum, but insoluble 
in the usual solvents of that substance, are sometimes found; and, as 
already noted, petroleum is always found among the products of its 
distillation. 
Careful study of the stratigraphic relationship of these shales by the 
U. S Geological Survey, has shown them to belong to the Green River 
