44 TJic American Geologist. January. is99 
the easy cleavage the direction of the cleavage lines is posi- 
tive with respect to the axis (>'/g) of the quartz plate. Its 
double refraction is about the same as that of augite, but its 
refraction is less. This mineral is supposed to be bovvlingite 
described by Hannay in 1877. (Min. Mag. I, 154). 
Localities. Reaver Bay; Little Marais; Terrace point, and 
many other places. 
THE LAWS OF CLIMATIC EVOLUTION.* 
By Marsden Manson. 
The objects of this paper are, to formulate the laws of cli- 
matic evolution, and to show: 
1. That in consequence of these laws a hot spheroid, 
holding water and air, or fluids of similar properties within 
the sphere of its control, and revolving about a source of 
solar energy, will be subjected to a series of uniform climates, 
gradually decreasing in temperature, and terminating in an 
Ice age; that this age will be succeeded by a zonal distribution 
of climates, which, within certain limits, gradually increase in 
temperature and extent. 
2. That the diflficulties met in the attempts to interpret 
present glacial and pre-glacial climates have been due, in 
]iart, to a failure to give due weight to certain of these laws, 
and to recognize the force of others. 
In attempting to trace the history of the earth back into 
the infinite past, the first step brings us in contact with the 
{juestion: What was the cause of the Ice age? Before going 
farther it might be well to glance at the theories which have 
been put forward to account for this age. and to brieflv con- 
sider the present position of the scientific world as regards 
this first step in the problem. It is not necessary to review 
all the theories which have been urged.f The principal ones 
only will be mentioned in two classes. Class I embraces those 
*Read before the British Association for the Ad-\'ancement of Sci- 
ence, Bristol, 1898. 
tSee The Climatic Controversy, S. V. Wood, Jr., Geol. j\lag., 1876 
and 1883. 
Report British Assn., 1892, p. 708. 
The Great Ice Age, Ed. 1894, Chap. IV., Dr. Prof. Geikie. 
