No. 6.] UPHAM — GEOLOGY OF NEW HAMPSHIRE. 329 



cover its area near the close of the glacial period than would at 

 that time remain in other parts of the State to the east and west. 

 The ice-sheet probably formed a high mountain-like ridge over 

 this lake, after it had disappeared from the basin of Ossipee lake 

 and from the lower part of the Merrimack valley. The ice cur- 

 rent was thus changed in direction on the east side of Winnipi- 

 seogee lake, and the last strise marked on the ledges differ much 

 from the prevailing course, being deflected towards the east, or 

 even to the north of east. As the melting continued, drainage 

 was frequently obstructed, because the ice-sheet retreated from 

 the lines of watershed towards the middle of this hydrographic 

 basin. The water seems then to have melted large open spaces 

 beneath the ice, near its margin, in which beds of clay and sand 

 were deposited. This would occur at the various heights and in 

 the situations where these beds are found, and the till which 

 overlies them is shown by its material to be that which was con- 

 tained in the ice-sheet, and fell upon the surface when its melting 

 was completed. 



Near the coast, beds of fine gravel, sand, or clay, sometimes 

 enclosing marine shells, are in several instances overlain by 

 upper till, giving evidence of a retreat and subsequent advance 

 of the ice-sheet. Doubtless the ice resisted the influence of the 

 warmer climate and changed conditions before which it disap- 

 peared, continuing late like the snow in spring. Its departure 

 at the last was correspondingly rapid, and was closely followed 

 by the hardier forms of vegetable and animal life. 



The abundant deposition of drift, both stratified and unstrati- 

 fied, which took place during the final melting of the ice-sheet, 

 has been brought into due prominence by Prof. James D. Dana, 

 who denominates this the Champlain period, deriving the name 

 from the marine beds of this era, which occur on the borders of 

 Lake Champlain. It is probable that this final melting took 

 place mostly upon the surface, which was thus moulded into 

 basins and valleys ; and near the terminal front of the ice, these 

 appear to have coincided closely with the contour of the land. 

 At last the surface of the ice became covered with the abraded 

 material which had been contained in its mass, and which was 

 now exposed to the washing of its innumerable streams. Its finer 

 portions would be commonly carried away ; and the strong cur- 

 rent of the rivers which would be formed near the end of the 

 ice-sheet could transport coarse gravel, or even boulders of con- 



