Page:The Journal of geology (IA journalofgeology11893univ).pdf/128
found in the later series, with which they are doubtless in part continuous.
The granites and gneissoid granites are placed together, because between the two are constant gradations. If one speaks accurately and includes among granites only those rocks which are completely massive, the gneissoid granites include the greater part of the granitic rocks; for in large exposures it is usually possible to find some evidence of foliation. The granitoid areas are of greatly varying sizes, running from small patches to those many miles in diameter. When everywhere surrounded by the schistose division of the Basement Complex, they frequently have oval or ovoid forms. In nearing the outer border of the granitoid areas, the foliation often becomes more and more prominent, and near the edge of an area the rock frequently passes into a well laminated gneiss.
The schistose rocks include fine grained hornblende-gneisses, mica-gneisses, chlorite-gneisses, and various green schists, formerly supposed to be sedimentary, but now known to be greatly modified basic and acid igneous rocks. These schists have usually a dark green or black color, are strongly foliated, and the variations in strike and dip of this foliation, within small areas, is very great. Not infrequently the schistose rocks are traced by gradations into massive igneous rocks.
The contacts between the schistose division and the granitoid division of the Basement Complex are usually those of intrusion, the granitoid rocks being the later. In passing from a schistose to a granitoid area, small pegmatitic looking veins of the granite are first found. In going onward these veins become more numerous and, after a time, unmistakable dikes of granite appear, which multiply in number and size in approaching the granite area, until the granite is found in great bosses. Here we have perhaps a nearly equal quantity of schistose and granitoid rocks, and in this intermediate zone the schists may be found as a mass of blocks within the granite, sometimes at but small distances from their original positions, the whole having frequently a somewhat conglomeratic appearance. However, these pseudo-