.">4 The American Geologist. July, 1394 
groundmassof hornblende granite. The spheroids are more basic than 
the groundmass. Thej contain four zones, the first or outer of which 
is characterized by magnetite grains in a mass of oligoclase; the second 
has hornblende and biotitc in large amount and oligoclase; the third is 
thf broadest and consists of radially arranged oligoclase with small 
amounts of quartz and orthoclase; the center is almost free from dark 
minerals and is essentially quartz and orthoclase. Tin- second type 
(from Balungstrand) has a coarse groundmass of microcline and quartz 
and some idiomorphic biotite. The spheroids are characterized by large 
oligoclase crystals: toward the periphery biotite is common, and the 
center is composed of microcline and quartz. Some remarks follow <>n 
the formation of the spheroids, especially in reference in the liquation 
theory of differentiating magmas. u. s. 6. 
Tht Ihmsselaer Grit Plateau in New York. By T. Nelson Dale. 
(Thirteenth Annual Report. U. S. Geol. Survey, pp. 291-340, pis. 97-101, 
1S94.) In this paper the geology of the eastern and central parts of 
Rensselaer county. X. Y.. is discussed. The author's interpretation of 
the general structure of the region is given in a section from Mt. Grey- 
lock in Massachusetts, on the east, to the Hudson valley at Poestenkill 
on the west. The broad limestone (Stockbridge) belt west of Mi. Grey- 
lock dips westward under the Taconic range, which here is a s\ nclinal. 
with two auticlinals, composed of a thickness of about 2,000 feet of 
Berkshire schists. The limestone again comes to the surface in the 
Berlin-Stephenson valley, on whose west side it dips under a small 
thickness of the Berkshire schists which are overlain by the Rensselaer 
grits; these extend westward for about ten miles, when the Hudson 
River shales (the equivalent of the Berkshire schists) emerge from be- 
neath them. The Stockbridge limestone is stated to be Cambro-Silurian 
in age, and the Berkshire schists Lower Silurian (Hudson River). The 
Rensselaer gril occupies a plateau area, about 175 square miles in extent, 
in central Rensselaer county. The plateau is composed of grits with 
interbedded conglomerates and schistose and slaty rocks. In structure 
it consists of a well marked synclinal along its east side, a compound 
synclinal along its west side, and certainly one and probably several 
folds in the intervening area. Fossils to determine the age of the rocks 
of this plateau have not been found, but. on account of the area! rela- 
tions of tl|£ gril to the Stockbridge limestone and the evidence of an 
unconformity of portions of the grit mass to Cambrian if no< to Lower 
Silurian rocks, as shown by its pebbles, the grit is thought to be uncon- 
formable on the Berkshire schists and is considered to represent the 
( >neida conglomerat( — the base of t he Upper Silurian. 
Mr. Dale's paper is of special interest in giving the structure and geo- 
graphic distribution of the rocks of the Taconic range along the Mass- 
achusetts-New York line, and in giving details as to lithologj ami 
probable age of the Rensselaer grit rocks. However, there are some 
important points, especially in the stratigraphy, which it semis are not 
full} established, or are simph assumed from insufficient evidence; we 
have reference to the age of theStockbridjre limestone and the I! ;rkshire 
