J. D. Dana on American Geological History. 309 
The order then reads, the Age of ae gree oc coreg 2 of 
AcRroGENS or Coal plants , of Reprines, of Mam 
_ The limits of these ages are as dgane as sbi Epa of: 
h 
aused universal grief to science, 4 that the Reptilian 
as an age of diminished life, between the two extremes in time, 
Palseozoic and Mammalian Ages. But, in fact, two grand 
divisions of animals, the Molluscan and Reptilian, at this time 
reach their climax and begin their decline, and this is the ear- 
instance of the highest culmination of a grand eae 
and formall announced in this country, in the Geologie Report 
_ of Messrs. Foster and beech although previously admitted 
- inan aniletinite w by most geologists. 
is q _ It embraces all I the lowest oa whe to the Silurian, for much 
é lowest granite cannot be exclu 
: e actual absence of animal life in tthe so-called Azoic Age 
_ + in this country is rendered highly probable, as Foster and Whit- 
3 ey atone by the fact that many of the rocks are slates and 
nm ‘ie em fossiliferous Silurian ‘tock, and yet have no 
and fa fide ad to a great extent crystallized « on a vast scale, 
a the first Silurian Ia layers were deposited. A grand revolu- 
tion is here indicated, pie ie the closing event of the early 
oe Bc history of the globe.t 
: as DW the Geology of the Lake Superior Land District, by J. W. Foster 
: Whitney, U.S, Geologits Part TL The Iron Regions together with Gen- 
cutive Document, "No. 4, Special Session, March, 1851. 
printed, March 13,1851. 406 pp. 8vo, with many plates, and a large 
I map and section. 
Whitney o it. pp. 7, 26, 182,) that at Chippewa Isla 
Menomonee rer sear 04°88 82 W) the Potsdam ignors ; sandst fovog 2 mp up- 
d Azoic elaton.. At Whi Raps lower down See a sam 
the of ce quartz Near le (not far from 
46° 85’ N, 87° 33° ot sinhilan contact of the nearly Sbeneotal Potsdam 
uartz rock is 
‘Austkh Gf thin tinent. wan well studied and defined at a still earlier date 
distinguished geologist of Canada, Sir William E, Logan. In his Annual 
