PRE-CAMBRIAN NORTH AMERICAN LITERATURE 369 
Collie * describes the geology of Conanicut Island, R. 1. The oldest rocks 
are a series of slates of unknown age, into which was intruded a mass of 
granite, porphyritic in character. This complex was exposed to weathering 
influences until a bed of débris lay upon its surface. This surface was 
depressed beneath the sea, and upon it was laid a great series of carbonifer- 
ous rocks. The complex was, therefore, the Carboniferous shore line. Into 
the Carboniferous rocks dikes were intruded, and both were folded, metamor- 
phosed, and have in many places become schistose. 
Wolff? reaches the following conclusions as a result of his detailed 
study of the Highlands of New Jersey in the vicinity of Hibernia. The rocks 
are found to consist of distinct bands of gneiss which can be recognized. 
These layers have once been nearly horizontal, and are folded into an anti- 
clinal dome which has the characteristics of ordinary folds, and has a distinctly 
recognizable pitch. The rocks of the series have a top and bottom, the latter 
being at the center of the dome and the top ones at the periphery. One char- 
acteristic horizon, a garnet-biotite-graphite-gneiss, must once have existed 
over a large part of the present area, and the same is probably true of the 
lower horizons. The foliation, in part at least, is parallel to the bounding 
planes of the different layers of rocks. The crystallization of the rock 
occurred during or after the action of the compressing force which folded the 
rocks and produced pitch but not before, since this structure is inherent in 
the shape of the minerals as they crystallized. These facts favor the view 
that the series is a sedimentary one, in which metamorphism and recrystalliza- 
tion took place contemporaneously with the folding and without fusion, and 
therefore that it is of Algonkian age. 
Keith? gives the geology of the Catoctin belt. The pre-Cambrian rocks 
constituting the Blue Ridge core are all of igneous origin. They include 
quartz-porphyry and andesite, Catoctin schist, and granite. A detailed litho- 
logical description is given of each of these rocks and of their alterations. 
The Catoctin schist and the granite are separated by areas in which the two 
are intimately intermingled. The Catoctin schist is an altered diabase, and 
the diabase is believed to be separable into two flows with a time gap between 
them. An evidence of this is a discordance of structure. The order of the 
events was probably as follows: (1) Diabase extrusion, (2) granite intrusion, 
(3) erosion interval, (4) quartz-porphyry and andesite flows, (5) erosion inter- 
*The Geology of Conanicut Island, R. I., by G. L. CoLLI£, Trans. Wis. Acad. 
Sci., Arts and Letters, Vol. X., 1894-5, pp. 199-230, with Pl. IV. 
? Geological Structure in the vicinity of Hibernia, N. J.,, by J. E. WoLrr, Geol. 
Sur. of N. J., Ann. Rep. for 1893, pp. 359-369, 1895. 
3 The Geology of the Catoctin Belt. by ARTHUR KEITH, Fourteenth Ann. Rep. U. 
S. G. S. (for 1892-3), Part IL., pp. 285-395; and Geol. Atlas of the U. S., Harper’s 
Ferry Folio. U. S. G.S. Washington, 1894. 
