The extent of the outflows of lava west of the Rocky Mountains is almost beyond comprehension. Literally, hundreds of thousands of square miles have been covered by them to a depth in many places of thousands of feet. These volcanic eruptions are mostly of late date, beginning in the middle of the Tertiary and culminating probably about the time of the maximum extent of the Laurentide Glacier. Indeed, so nearly contemporaneous was the growth of the Laurentide Glacier with these outflows that Professor Alexander Winchell had, with a good deal of plausibility, suggested that the outflows of the eruptions of lava were caused by the accumulation of ice over eastern British America. His theory was that the three million cubic miles of ice which is proved to have been abstracted from the ocean and piled up over that area was so serious a disturbance of the equilibrium of the earth's crust that it caused great fissures to be opened along the lines of weakness west of the Rocky Mountains, and pressed the liquid lava out, as the juice is pressed out of an orange in one place by pressing upon the rind in another. Professor Carpenter's view is the exact reverse of Professor Winchell's. Going back to those orographic changes which produced the lava-flows and the elevation of the northern part of British America, he thinks the problem of getting the moisture transferred from the Pacific Ocean to the Canadian highlands is solved by the lava-flows west of the Rocky Mountains. This immense exudation of molten matter was accompanied by an enormous liberation of heat, which must have produced significant changes in the meteorological conditions. The moisture of the atmosphere is precipitated by means of the condensation connected with a lowering of its temperature. Ordinarily, therefore, when moist winds from an oceanic area pass directly over a lofty mountain-chain, the precipitation takes place immediately, and the water finds its way back by a short course to the sea. This is what now actually occurs on the Pacific coast. The Sierra Nevada condense nearly all the moisture; so that very little falls on the vast area extending from their summits eastward to the Rocky Mountains. All that region is now practically a desert land, where the evaporation exceeds the precipitation. In Professor Carpenter's view the heat radiated from the freshly exuded lava is supposed to have prevented the precipitation near the coast-line, and to have helped the winds in carrying it farther onward to the northeast, where it would be condensed upon the elevated highlands, upon which the snows of the great Laurentide Glacier were collected.