140 A. Winchell on Pressure of a Continental Glacier. 
point out escapes of molten lava as sequences to sedimental 
pressure; but geologists have not done this in any articulate 
way ; and the principle involved is one of the points at which 
1 aim in this memorandum. 
One of the great doctrines of geological science which have 
found their way into common knowledge and acceptance, is the 
doctrine of former general glaciation of the north temperate 
lands. North America, east of the Rocky Mountains, and as 
far south as Cincinnati, was covered by a sheet of glacier ice, 
which perhaps averaged a mile in thickness. Its pressure upon 
the earth's exterior will readily be understood as enormous, and 
the reader can easily reach a numerical result. It will be borne 
in mind that the whole weight of the ice assumed the form of a 
pressure; while in the case of ocean-sediments, whose effects 
xire generally admitted, the buoyant action of the sea-water 
prevents about half the weight of the sediments from assuming 
the form of a pressure in excess of that already exerted by the 
water. 
Now where was the region subjected to protrusion in re- 
sponse to the enormous pressure of the great ice-mass? The 
view which I wish to enunciate is, that some of the region west 
of the Rocky mountains was the theatre of actions responsive 
to the great eastern and northern pressure. It is established 
that those regions were not generally glaciated. They must 
consequently, have experienced a tendency to become protu- 
berant. Some regions may have been bodily uplifted. If 
fractures were thus caused, an escape of molten matter may have 
permitted such regions to subside. There are evidences of 
simple vertical actions and movements such as would thus result. 
If, however, fissures existed, or were produced, through which 
outflows of lavacould take place, then instead of a vertical eleva- 
tion of the crust, a flood of lava would cover the country. 
Such floods of lava have occurred. Vast sheets of frozen 
lava are the most conspicuous featui"e of a region embracing 
large parts of Washington, Oregon, Idaho, Nevada, California, 
Arizona and New Mexico. In Oregon and Washington there 
was an almost universal flood of molton material, which covered 
and buried the whole original face of the country — hills and 
<lales, mountains and valleys. Its extent is estimated by Le 
