Geology and Natural History. 241 
of a battery. They remark that the current from the latter was 
sufficiently constant. -In order to show, however, the fluctuations 
in current caused by irregularity in the contact of the brushes of 
the machine, and want of constancy in the speed of rotation, they 
enclosed a tube filled with bisulphide of carbon in a coil; polar- 
ized light was sent through this tube and the light was after- 
ward viewed by means of a spectroscope. The apparatus was 
und Chemie, No. 6, p. 257, 1880. as. 
Il. GroLoey anp Natura History. 
1. Geological relations and fossil remains of the Silurian Iron 
es of Pictou, Nova Scotia—Dr. J. W. Dawson, in the Canadian 
Naturalist (vol. ix, No. 6), gives an account of these ore beds with 
lists of fossils, and reaches the conclusion that the beds probably 
do not reach as far up as the Oriskany group (his former pub- 
lished view), but correspond in age with the upper beds at Avi- 
saig, which are Upper Silurian, “These deposits of iron ore 
a general fact in Nova Scotia, and along the Atlantic margin of 
orth America, though present farther west in Northern New 
equal or superior importance. : 
Am. Jour. Ss as Vou. XX, No. 117.—Sept., 1880, 
