1894. | NEW YORK ACADEMY OF SCIENCES. 187 
less worked over by water and subsequently altered by meta- 
morphic action. 
The present paper deals only with the lower series of rocks, 
the so called Laurentian, in the vicinity of the city of St. John. 
This area has been taken as a type,as it is well exposed, and 
atfords good opportunities for study. A great extent of coun- 
try both east and west of it is occupied by the same forma- 
tion, but is largely wooded, the rocks deeply buried by surface 
deposits, and roads are few and far between. 
The lower part of the Laurentian series, just north of the 
city, is made up of massive crystalline rocks, both acid and 
basic, which have been described as syenites, gneisses and dio- 
rites. The first of these is a coarse-grained quartzose granitic 
rock, with large porphyritic crystals of pink-weathering feldspar. 
Although its ‘resemblance to an eruptive granite was noted by 
the officers of the survey, yet it appears to have been considered 
a highly metamorphic sedimentary gneiss.* Microscopic study 
has shown it to be an intrusive quartz diorite or hornblende- 
granite. The gneisses proper are of variable character, at times 
quite massive, but generally schistose, granular, banded with 
alternate light and dark beds, and in the upper part of the 
series interbedded with the limestones and quartzites. They 
are accompanied by hornblende and mica schists, into which 
they sometimes grade. Thin sections show no trace of igneous 
origin. The diorites included a variety of rocks, some of which 
seem to be altered sediments, while others are altered igneous 
rocks, gabbros, quartz-diorites and diabases. Associated with 
the less crystalline limestones are numerous thin beds of a fine 
grained black pyritous rock, which has been generally called 
argillite; it is wanting in any noticeable bedding or slaty cleav- 
age. 
Microscopic study shows that much of this lower Laurentian 
series is of igneous origin, and that its exact age is very doubt- 
ful, though it is probably Pre-Cambrian. The intrusive rocks 
of the series, which it is the purpose of this paper to describe, 
are of two classes, one a very quartzose acid rock varying from 
a quartz-diorite to a hornblende-granitite ; the other quite basic, 
and varying from anorthosite to peridotite. These may be 
called respectively granite-diorite and gabbro. The first occurs 
as long ridges and more or less detached remnants covering 
altogether a considerable area. Of the second the exposures 
are quite limited, being confined to two small bosses, each only 
a few hundred feet long and wide, in the ‘‘ North End” of the 
city, commonly known as Indiantown. Other exposures are 
* Report of 1871. 
