On the Geology of the Northwestern Regions of America. 325 
11, —— muralis. 18, Cephalic shield of a Trilobite allied 
12, Orthis, sp.+ to Illenus arcturus. 
Lingula, sp.¢ 19. Pustulated cephalic shield of an 
14, Terebratula, sp.t Tienus, 
20, Conularia, sp. 
21, Several specimens of the shield of 
icauda. 
Norr.—Those marked + are figured in Dr. Owen’s Atlas of Illustration. 
Many of these, Dr. Owen states, “are identically the same 
fossils as occur in the lower part of ‘Formation No. 3,’ in Wis- 
consin and Iowa, in the blue limestones of Indiana, Ohio, Ken- 
tucky, and also in the Lower Silurian of Europe. The Coscino- 
pora is precisely the same as the coral which is particularly 
characteristic of the lower beds of the Upper Magnesian Limestone 
f Wisconsin. ‘The specimens of F'avosites basaltica cannot be 
distinguished from those which abound in the Upper Magnesian 
Limestone of Wisconsin and Iowa and the Lower Coralline beds 
of the Falls of the Ohio.” 
_Ithas been noticed that the limestones of this formation are 
distinguished by two different tints of color. From the following 
analyses of the two varieties published by Dr. Owen, it would 
appear that they differ also considerably in their mineralogical 
character. 
Anvlysis of the Compact Limestone from Red | Spotted and banded Limestone containing 
: Rive Lepiena. Cos 
r, containing Lepte ‘oscinopora. 
Carbonate of Lime ............ 53°7 | Carbonate of Lime .........-. 781 
nate o: rn eee 40°5 | Carbonate of Magnesia ........ 178 
Insoluble gg inte he 08 soluble matter ......-..++++ 10 
Alumina, Oxyd of Iron, and Man- Alumina, Oxyd of Iron and Man- a 
fanese ..., 0 eee ee: . 
Water and loss 1-0 | Water and loss ............-- 13 
100°0 100°0 
detected some Trilobites, a Maclurite, and a Coral, which last 
ossil from the description given of it may have been a Recepta- 
culites ; and it may be added, that Marcou, apparently on the 
authority of Mr. Logan, classes the limestones of Lakes Abbitibie 
and St. John as Lower Silurian. The limestones of the Kakabeka 
Falls were identified by himself as belonging to that division. 
The ins ciency of geological explorations, and the want of 
published documents, render it impossible as yet to define with 
any approach to accuracy the limits of the two great divisions of 
the formation in this part of America, while it may be safely 
asserted, however, that under one or other of its forms the Silu- 
