202 TRANSACTIONS OF THE [APR. 16, 
The character of the gabbroitic knob may vary through pre- 
ponderance of. different minerals, from peridotite through “ for- 
ellenstein,” olivine-norite, olivine-gabbro, or gabbro, into an- 
orthosite. In this great variation it is in contrast with the 
other Indiantown knob, which was probably uniformly an oli- 
vine-gabbro. It is much more altered than the one first de- 
scribed, and now is a gabbro-diorite, according to Prof. G. H. 
Williams’ nomenclature. Its notable pitted appearance fades 
out to the north, where its limits are not accurately known. 
Retations. The relations of the gabbro to the Laurentian 
series are not known. At the southern end the knob along the 
river-edge is separated from the limestone and gneiss by a peg- 
matitic mass of pink feldspathic rock, probably a “ granite vein.” 
Elsewhere it is surrounded by quartz-diorite of undoubtedly 
later age. The contact with this has been already described. 
There are two or three exposures within the area studied, of 
massive hornblendic rocks, which may perhaps be altered basic 
intrusives; but neither in the field nor in thin section could they 
be distinguished as such, and they are consequently mapped as 
of doubtful origin. 
GENERAL OBSERVATIONS. We have then, near St. John, the 
following types of Pre-Cambrian rocks: 
1. Limestone-gneiss, sedimentary series. 
2. Intrusive gabbro. Relations to (1) uncertain. 
8. Acid intrusives. Later than (1) and (2). 
4. Surface volcanics. Relations to (2) and (3) uncertain; 
probably later than both. Certainly later than (1). 
5. Hicheminian (sub-Cambrian) series. The Olenellus fauna 
not having been found to extend down into this series, the un- 
conformity between them and the St. John group must for the 
present be assumed as the base of the Cambrian. 
If the succession be as here arranged, it is in accord with that 
generally observed in eastern North America.* The metamor- 
phism is not very intense, the limestones usually retaining much 
of their blue-black color, and being of a grain about that of 
sandstone or ordinary marble. The gneisses are not very coarse, 
though sometimes quite massive; the surface volcanics are very 
like those of South Mountain, Pa., as described by Prof. Wil- 
liams,+ but, if anything, less altered. Whether any of the coarse 
and massive gneisses forming the “Archean complex ” exist in 
* Dr. Ellis has lately (Bull. Geol. Soc. Amer., 1893) emphasized the parallelism 
of the sedimentary rocks of southern New Brunswick with those of the Ottawa 
district ; this still holds, except that the lowest member of the series is wanting 
at St. John, and the intrusives of the typical Pre-Cambrian succession are 
present. 
+ Voleanie Rocks of South Mountain, in Penn’a. and Md. Amer. Jour. Sci- 
XLIV., p. 482, Dec., 1892. 
