222 
The American Geolos:ist. April, looi. 
ilar rocks of igneous origin, but the form and manner of weath- 
ering are those of igneous rocks. The more perfectly banded 
phases, — gneisses — weather in process and topographic outline 
closely similar to the massive granites. The chemical and 
physical processes involved in the disintegration and decom- 
position of these rocks are the same, and are described and dis- 
cussed elsewhere.* 
Resume: From the preceding facts, there can apparenth 
be little question as to the origin of the granites and their band- 
ed equivalents. The rocks appear like eruptives in the field. 
The clastic grains, when present and seen in thin sections of 
the foliated phases — gneisses — are evidently dynamic in ori- 
gin ; all are sharply angular, and none have the outline of 
water-worn grains. The structure of the gneisses is similar to 
that of like rocks occurring elsewhere, and shown to be meta- 
morphosed eruptives. Therefore, since they conform with 
such regularity in mineral and chemical composition, and field 
evidences as well, to the massive granite type, there can be no 
reason for believing them to be anything but altered igneous 
rocks. No evidence of any kind is, at present, apparent to 
support the belief that the gneisses so far studied are water- 
deposited sediments, subsequently recrystallized by metamor- 
phic processes. 
As to the origin of the massive granites and their equiva- 
lent, porphyritic phases, there can be no doubt. 
Structural features : The structural phases of the var- 
ious granite types have already been noted. Joint planes are 
very common in many of the larger masses and are as a rule, 
only slightly developed in others ; and they traverse the rock 
with great regularity. They may conform to several different 
directions but usually they have uniform directions over the 
entire region. The best developed ones have nearly due east- 
west and north-south courses, approximating in some quarries 
northwest-southeast directions. Considerable subsequent 
movement in the granite-masses is manifested in many of the 
larger quarries, in pronounced slicken-sided surfaces of the 
joint planes. The slickened surfaces are, as a rule, coated with 
* Read by title at the Albany, N. Y., meeting of the Geological Soc. ofAmer., 
and presented in abstracted form liy Dr. Geo. P. Merrill. 
A preliminary report on the granites and gneisses of Georgia by T. L. 
Watson, Geol. Sur. of Ga., in press. 
