18 TRANSACTIONS OF THE [ocr. 19, 
weight with the writers. The other is that it represents only the 
upper portion of a dike, and thus contains the float-material which 
the advance of an igneous body would naturally gather from the 
walls. The lack of such inclusions in the neighboring dikes may be 
due to the fact that their tops have been eroded. A still different 
view has been advanced by Pres. Hitchcock as applicable to a second 
similar dike, to which we now pass. 
This second dike is much narrower, and is found on Nash’s Point, 
some miles south. It is about twelve feet wide, and consists of 
somewhat rounded fragments of Archean norite, red Cambrian 
quartzite, and Hudson River slate, chiefly gathered in the middle 
portion, and all cemented together by the bostonite ground-mass, 
whose analysis was given above. President Hitchcock’ mentions, 
also, gneiss, hornblende-schist with garnets, quartz, gray sand- 
stone, and black Trenton limestone. Probably what he called 
granite we have called norite. The slides of norite and quartzite 
exhibit dynamical effects of a marked character, as the crystals have 
been strained and shattered. These inclusions indicate a deep- 
seated source for the igneous rock—at least beneath the norites and 
gneisses, and one or two inclusions in a basie dike from Burlington 
indicate the same for the basic dikes. President Hitchcock was 
impressed by the rounded, or, as he interpreted it, the waterworn 
character of the inclusions. He was led by this to regard the dike 
as originating from acrack which had become previously filled with 
débris from above. This débris he considers to have been partially 
melted or sintered in the metamorphism of the region. As some of 
the boulders are limestone, and as there are many undoubtedly intru- 
sive igneous dikes within a few feet, we regard the rounded character 
as due to partial absorption, and consider the foreign bodies as inclu- 
sions. Brecciated porphyries formed of a broken eruptive rock that 
has been re-cemented have been mentioned by Pumpelly from Pilot 
Knob’? and by Crosby’ from eastern Massachusetts, but the phe- 
nomena are obviously different from those here described. 
The Basic Dikes. 
The basic dikes are all compact, dark rocks, that to ordinary 
microscopic examination, give almost no indication of their consti- 
tution. The only apparent minerals are feldspars in the coarser 
diabases, and an occasional glistening hornblende or augite prism 
in the more basic dikes. The thin sections exhibit a series of 
mineralogical mixtures extending from very typical ophitic diabase 
through camptonites, in which the dark silicates beeome idiomorphic, 
and the feldspars recede, to aggregates of augite and hornblende, 
1 EK. Hitchcock, On Certain Conglomerated and Brecciated Trachytic Dikes 
in Vermont, ete., Proc. A. A. A.S., xiv, 156; Geol. of Vermont, vol. ii, p. 583. 
2 R. Pumpelly, Geological Survey of Missouri, Preliminary Report on the 
Iron Ores and Coal Fields. E. Haworth, Missouri Geological Survey, 1891, 
Bull. v. 
3 W. O. Crosby, Geology of Eastern Massachusetts, p. 50. 
