Geology and Natural History. 311 
Journal (xxvii, 488) is now followed by a no less valuable com- 
panion volume on Light. is volume is the more welcome since 
contributions to the department of physics of which it treats, 
of a general nature, have be w in recent years, while there 
to supplement the instruction of the elass-room. It is fresh in 
matter and clear in style. valuable feature, and one which is 
of necessity absent in class-room text-books, is to be found in the 
attention given to the historical development of the subject ; num- 
erous quotations from Newton, La Place, Huyghens and others 
are calcula o make clear to the student how the present 
accepted principles and theories have been reached. 
Ill. Grotogy anp Naturau History. 
1. Professor James Hall on the “ Hudson River” age of the 
Taconic slates.—At the meetings of the American Association of 
lean Association) 40 5 years age of the Taconic 
System was the subject of long discussions; and in the course of 
m Profe all advocated, in opposition to Professor Em- 
mons, the Lower Silurian age of the Taconic slates and lime- 
Stones, citing facts in proof from his own investigations. No 
Paper on the subject was published by him, and not even a report 
h - 
Saddle Mountain and Graylock (as also shown by Emmons) ; in 
the second, Mt Anthony is proved to a broad synelinal of 
Slates with limestone ben ath; and in the third, Equinox Moun- 
tain is anoth synclinal ate with underlying limestone— 
thus long antic ipating in the exhibition of these broad synclinals, 
the similar sections t ont Geological Report (1862). 
Underneath each section the limestone is stated to be of the age 
18) . 
are made, as necessarily foll 
Stone, of later Lower Silurian or the Hudson River group. The 
slates at Hoosick River had been previously proved to afford 
