428 Brooks and Pumpelly—Age of the 
also placed decidedly farther forward, and its neck segment is 
much less distinctly defined. hen we come to its thorax, we 
also see equally well marked differences, its pleura not being 
curved backward and falcate as in that species, nor having their 
furrows extending so far outward. It almost certainly has one 
or two segments less, though the slight slipping backward of 
the cephalic shield leaves some little room for doubt on this 
point. I have, however, also an inferior specimen before m 
belonging to the collection of Dr. H. H. Hill of Cincinnati, 
believed to belong to this species, and this certainly has only 
eight thoracic segments. Again, the pygidium of our species 
differs in having distinctly flattened, smooth, and very obscure 
furrowed segments on the lateral lobes, that do not extend out 
ward upon this border, while on that of P. parviuseulus the 
segments are strongly defined, without furrows, and extend very 
oe or quite to the border, so as scarcely to leave any flat 
tened margin. 
The specific name is given in honor of T. W. Spurlock, Hit, 
of Cincinnati, who discovered some of the new fossils loan 
to the Ohio Survey, and is well known in that city for his long 
devotion to the study of the natural sciences. | 
Lecality and position.—Cincinnati group of the Lower Silt: : 
rian, at a horizon of about 100 feet below the tops of the hill — 
at Cincinnati, Ohio. Mr. Dyer’s collection. 
Art. LVL—On the Age of the Copper-bearing Rocks of Lake : 
Superior ; by T. B. Brooks and R. PUMPELLY. 
SomME observations made by us in the southwestern ye 4 
the Upper Peninsula of Michigan demonstrate a wide d 
in age between the Cupriferous series of sandstones, conglom- 
erates and melaphyres on the one hand, and the Lower Silurian 
sandstone, with which they have generally been considered a8 
nearly identical in age, on the other. Both series et ben 
referred by Foster and Whitney:to the Potsdam, by > 
liam Logan to the Chazy, while Mr. Bell of the Canadian Comps ie 
considers the Cupriferous series to be Triassic, the latter pees : 
ing herein with Jackson and with the view afterwards 
doned by Owen. 
The principal facts on the south shore of Lake Supe : 
as follows: A series of red sandstone and shales, Ly ce 
where nearly ge Cromrpee'e borders the Michigan —_ Pi 
the Saulte St. Mary and Béte Gris Bay on Keweena 
From the former place to west of Grand Island, this sands" 
is overlaid on the south by other Silurian rocks, and Deb" 
