178 The Americun Geologist. Scptomhor, ]89(> 
THE BLACK RIVER LIMESTONE AT LAKE 
NIPISSING. 
I!.v N. H. WiNriii-.i.i.. 
On the occasion of the meeting of the American Association 
for the Advancement of Science at Toronto in 1889 an excur- 
sion was made to the region '>r lake Nii)issing, whicli was at- 
tended by the writer. Subse(|uent]y a small collection of 
fossils from the islands of this lake was procured through the 
aid of Mr. 'J\ D. Ledyard, escj., of Toronto. They were 
put in the possession of Mr. Ulrich, Newport. Ivy., who has 
recently furnished the following identilications. 
The islands of lake Nipissing are briefly described by Alex- 
ander Murray in his geological re])ort for 1854, and the is- 
lands themselves are represented on his map accompanying 
his report, sheets 8 and 10. This limestone is found on one 
of the islands of the Manitou group, in the east-central por- 
tion of the lake, and on Iron island, in the western portion, 
and it probabl}^ underlies much of the lake between. On the 
Manitou island it rests unconformably on gneiss and trap 
rock, which constitute the larger portion of the island, show- 
ing a thickness of over six feet, in the lower portion being a , 
siliceous limestone * * * '-liolding- Orthoceras. with a few other 
obscui'e fossils and small angular fragments of the altered neck on which 
it rests. Over the sihceous bed are alternations of blue and gray lime- 
stone and shale, holding numerous fossils, among which are orthocera- 
tites and shells, both univalve. and bivalve, but all too obscurely defined 
to admit of correct identification: the orthoceratites, which are very 
numerovxs in all the beds, strongly resemble the Ormoceras tcuuijUuni of 
Hall, given by that author as a characteristic species of the Black River 
formation. These beds occur on the S. W. end of the island and show a 
gentle dip toward the S. W. 
On the west side of Iron island beds of red and gray sandstone rest 
unconformably on gneiss and crystalline limestone, dipping at the north 
end of the exposure S. 30° W. <4°. and at the south end S. 75° W. <3'-' 
to 5°. The lowest beds of the sandstone are red, with small round 
green spots occasionally dotted over the surface: the sandstones are 
coarse grained and the beds vary in thickness from six inches to two 
feet. The upper beds are yellowish-gray and sometimes whitish, and 
occasionally appear to be slightly calcareous. They ai-e mostly of coarse 
grain, at times becoming a tine conglomerate. Small subspherical con- 
cretions are common to the upper beds, and on one occasion an impres- 
sion resembling the obscure coat of an orthoceratite was observed on an 
exposed surface. Some of the beds are pr<>l)ably well adapted for 
grindstones. 
