Review of Recent Geological TAterature. 63 
REVIEW OF RECENT GEOLOGICAL 
LITERATURE. 
Some Maryland granites and their origin. By Charles Rollin 
Keyes. Bulletin of the Geological Society of America, vol. iv, pp. 299- 
304, with a plate; July 31, 1893. The eastern part of the Piedmont belt 
in Maryland is described as consisting chiefly of gneisses broken 
through in many places by eruptive rocks, as gabbro, diorite and pyrox- 
enite, until these basic eruptives occupy fully half of the present ex- 
posed surface. The granites are found in small areas, to the number 
of a dozen or more, intersecting both the foregoing igneous rocks and 
the gneiss. Although these granites have been held by some in- 
vestigators to be metamorphic from mechanical sediments, the author 
confidently maintains their irruptive origin from an acidic molten 
magma cooling under pressure. Sometimes, as at Dorsey's Run, the 
granite is seen to have been forced between beds of twisted and puck- 
ered gneiss, and at Woodstock huge blocks of gneiss are enclosed in 
the granite. At Sykesville a great variety of fragments of foreign 
rocks, from minute pieces up to blocks of large size, occur as inclusions 
in the granite, comprising limestone, soapstone, pyroxenite, vein quartz, 
and hornblendic and bi'otitic gneisses. All these rocks are well repre- 
sented in outcrops several miles eastward, where they dip to the west. 
In most of the fragments the outside to a depth of two to four centi- 
meters or more is much changed, but the interior of the larger pieces 
often or commonly exhibits the rock in its original character. Aside 
from the usual microscopic indications that the granites have cooled 
from fusion, another evidence of this is afforded by large grains, micro- 
pegmatitic intergrowths of quartz and feldspar, which appear to have 
been rounded and occasionally hollowed on their sides by magmatic 
corrosion. 
Epidote as a Primary Component of eruptive rocks. By Charles 
Rollin Keyes. Bulletin, G. S. A., vol. iv, pp.305-312, with four figures 
in the text; July 31, 1893. The epidote of certain Maryland granites is 
found in isomorphous growths with allanite, as well as in separate well- 
defined crystals. That it must be there an original constituent, and 
not a secondary product, appears from its presence in perfectly fresh 
rocks, or those which have been but slightly altered by orogenic move- 
ment; by its inclusion in sphene, one of the first minerals to crystallize 
from the molten magma; and by its sharply defined crystallographic 
faces, completely mantled by unaltered biotite or feldspar, and giving 
shape to these essential components of the granite. 
Relations of the Laurentian and Huroniaii rocks north of Lake 
Huron. By Alfred E. Barlow. Bulletin, G. S. A., vol. iv, pp. 313- 
332; August 4, 1893. This paper is a revision and extension of one pub- 
lished by Mr. Barlow in the Am. Geologist of July, 1890. The Lau- 
rentian gneiss and granite are shown to have been irruptive and in a 
