In his lecture of last Monday night, Prof. Wright gave the results of his own researches for facts to work out the details of Prof. Agassiz's already proved Glacial Theory. He had himself located the southern boundary of the great ice sheet, which once covered the northern half of this continent, by means of the great heaps of sand and gravel called terminal moraines, pited up by the ice where its progress was stopped. These heaps are sometimes very large, one in Pennsylvania is 150 feet high and 12 miles long, Nantucket and Martha's Vinevard are also terminal moraines. The southern limit, from New Jersey to the Pacific, of this ice-sheet was shown by maps; and, curiously enough, this line also bounds the great wheat fields of the country, the area once covered with ice being far more productive than the rest.
A number of views of glacial scratches and the pebbles which made them were next shown, while the cause of their formation was being explained. Then pictures of glacial deposits some 95 feet thick were presented. Cedar logs of large size are often buried in these and the lecturer said that while camping in Alaska his only fuel was preglacial woods many thousands of years old.
Photographs of Alaskan scenery were next exhibited in great abundance, including some of Sika and of the various mining camps. The coast is a range of semi-submerged mountains, and the whole country is "set up on end." The precipitation at Sitka is very great, often reaching 100 inches, and it often rains there 2 5 days in the year. This weather is most favorable to the formation of glaciers, and the rest of the lecture was devoted to one of the most noticeable-the great Muirglacier. This is one mile across and 408 feet high where it reaches the sea, while the water is there 600 feet deep. Great pieces of ice continually break off with a loud noise, and these icebergs cover the surrounding inlets. The motion of this mass was from 65 to 72 feet per day in places, and the whole moved at an average rate of 40 feet per day about the same as the Greenland glaciers. The erosion of these glaciers is very great. It is calculated that the sub-glacial streams lower a surface of 1,200 square miles-one-third of an inch each year.
Many entirely novel views appeared, and the speaker was extremely entertaining throughout the whole lecture. Professor Shaler, President Eliot, and many others of the faculty were present.