310 J.D. Dana on American Geowgical History. 
r these ea remarks on the divisions of Geological — 
time, I now propose to take up ‘the characteristic features. and ae 
succession of events in American Geology. a 
Report for 1846, oat and that for 1848, he points out several e sample of the AJ 
Silurian covering the contorted Azoic, and his subsequent surveys have o>." 
facts of this kind. The occur = of the lakes Huron and Superior, and along — iy 
and to the north of the St. Lawr Movers in the vicinity of the lakes just men- 
tioned, he foun oe the Azoic divided i to two unconformable groups, a lower, since oy 
called by him the Laur 5 n upper, the Huronian; the former consisting 
granite, sy ‘ st reat rock, hypersthene rock, | es 
ete.; the latter of diorite, slates, white and — sandstones, conglomerates, lime- 
stones, the whole much intersected by trap and metalliferous ve ng native 
copper, cic. and having a thickness in some paces, pol “3 9000 to 12000 feet. 
vedying:! the Azoic, a8 
observed by him in the vicinity of the St. Lawrence pes of Lake Champlain, 
are oh in the Quarterly Journal of the Geological Society of eke, for 1852, 
pp. 2 
In the progress of the Geological Survey of New York, commencing in 1836, the 
fact that the crystalline rocks of Northern New ex were older than the Silurian 
i braid shown, but good sections illustrating the superpositions of the two were 
rath set meeting of the American Association at Cincinnati in 1851, when Foster 
and Whitney first prese thre Siaise Siieskonn Prof. Mather stated that he 
had traced the continuation of the system nearly to the sources of the 
CAE: pee 
Assoc. Rep. 1851,) indicating the inferiority in position of these come Hom ene 
as had been 1 by Messrs. Foster and Whitney from the investigations 
Mersch under t! eir m; and Dr. Sp. ann described related rocks in 
* The evidence with respect to the existence of cary in the Azoic Age, though 
by no means positive, is stronger than here gaa d.—In the first pista these oe 
er ages were | 
, ‘efe; 
noted that — has been observed growing mong 
in waters having a temperature of 180° F, pe heneittes in seen a case of sim 
on ida one of the Philippines, where the tem mperature was 160° a 
much beyond the limit, which the eggs of animals can endure and survive. ; 
