294 THE POPULAR SCIENCE MONTHLY. 



and he finds the evidences of the dissolution of the ice-sheet multiply- 

 ing. Occasional streams of water run on the surface of the ice, or 

 plunge into some of its openings. Deep gorges reveal multitudes of 

 fragments of rock frozen into the ice, and occasional bands of dirt and 

 gravel embraced in the solid ice. The surface is everywhere dirty, or 

 perhaps muddy, from the wasting away of the surface of the glacier. 

 He meets frequent openings, in which generally water may be seen or 

 heard. Into these gorges the debris slides down the sloping sides, in- 

 creasing the insecurity of his footsteps. Still farther south, the gen- 

 eral surface is covered with a pulpy earth, mingled with stones and 

 bowlders. The ice is evidently much attenuated. The areas of firm, 

 uncovered terra firma are wonderfully increased in size and frequency. 

 The ice itself is crowded into the valleys, or, if it be in a broad, level 

 tract, like the State of Minnesota, the surface is covered with the 

 debris of the conflict of ice with earth, the ice itself being visible only 

 in those places where crevasses reveal it, or where deep gorges are 

 worn by running streams. Travelling still farther south, the explorer 

 would come upon large areas in which he would not be able to know 

 whether the glacier underlay the superficial drift or not. If he were 

 to stop on one of those wide areas, and make his latitude and longi- 

 tude certain, by a series of astronomical observations, he might find to 

 his surprise, after a few years' residence, that his observatory and ap- 

 paratus had been bodily carried, by an imperceptible motion, some rods 

 to the south. If he were to penetrate the earth on which his foothold 

 seems so steadfast, he might find, equally to his surprise, that he was 

 still riding on the surface of a vast ice-sheet, the earth and soil of 

 which may have furnished him annual crops of potatoes and barley. 

 In other places in the same latitude he would find the ice laid pare 

 over considerable areas, washed clean by the drainage incident to the 

 dissolution of the glacier. The turbid streams would be vastly larger 

 than those which occupy the same beds to-day. They would run with 

 tenfold more violence. The drift-materials would be freed from the 

 clayey portions, and be spread along their channels in curious and 

 varying assortment. In some places the thickness of the whole sheet 

 of drift would be brought under this washing and stratifying process. 

 In others, the ice gently dies out, and lets it down on the rocky surface 

 without any change from the condition in which it lay on the glacier. 

 If, at last, the explorer travels far enough south to actually leave 

 the area of the glacier, what is the condition of the surface ? It is 

 plainly one of glacier-drift. In some places he will find the various 

 parts, such as gravel-stones, sand, clay, and bowlders, confusedly min- 

 gled, showing no assortment or stratification. The clay which has re- 

 sulted from the grinding action of the glacier on the surface on which 

 it lay, from dust blown over the ice by violent winds, as in the Alps, 

 and from the sediment washed on the ice from the higher knobs that 

 first became uncovered, fills all the interstices so closely as to make of 



