1894. | NEW YORK ACADEMY OF SCIENCES. 209 
oxide of zine were found two pyramids of the first order 2 P 
and } P, the pyramid of the second order } P and the unit prism 
of the first orders P. The notes will be elsewhere printed. 
The papers were discussed by Messrs. Hovey, Whitfield and 
Kemp. 
The next paper, by Prof. C. H. Smyth, Jr., was read by the 
Secretary in the absence of the author. 
A GROUP OF DIABASE DIKES AMONG THE THOU- 
SAND ISLANDS, ST. LAWRENCE RIVER. 
By .C.-H. Smyra, Jm. 
The presence of a number of dikes cutting through the gran- 
ites and gneisses of the Admirality Group of the Thousand 
Islands was mentioned by Dr. A. P. Coleman* about two years 
since. Through the kindness of Dr. Coleman the writer was 
put in possession of many details in regard to the occurrence of 
the dikes, which greatly facilitated an examination of the region 
during the past summer. 
The islands included in the group referred to lie within three 
miles of the village of Gananoque, Ontario, and, as described in 
the paper cited, consist of granite, gneiss and quartzite, over- 
laid on the eastern side of the group by Potsdam sandstone. 
The dikes do not break through the sandstone and hence must 
be older than upper Cambrian and younger than the granite 
which is itself intrusive in the gneiss. No other limitation can 
be put upon their age. 
The rock of which the dikes consist is very dark colored and 
strongly contrasted with the light red of the surrounding granite 
and gneiss. On the mainland west of Gananoque and on the 
adjacent islands thirty-nine dike outcrops were noted, but in 
several instances the relations of the outcrops were such as to 
indicate that two or more of them were parts of single dikes, 
continuous under the intervening river channels. Allowing for 
this duplication it is probable that not more than thirty distinct 
dikes were examined. There is great likelihood that some dikes 
were overlooked, but those examined were so distributed over 
the region that they must give a complete representation of the 
general character of the rocks. All of the dikes strike about 
north and south, and, so far as can he ascertained, are nearly 
*A P. Coleman—Some Laurentian rocks of the Thousand Islands, Can. Rec. 
Scie Vi...) pel 27. 
Taineionons N. Y. AcapD. Scr., Vol. XIII., Sig. 14, August 6, 1894. 
