GLACIAL DRIFT. 305 



plainly marked for a distance of three hundred miles, reaching from Truro, near the 

 end of Cape Cod, through Barnstable, the north-west part of Martha's Vineyard, Block 

 Island, Montauk Point, the centre of Long Island, the south-east part of Staten Island, 

 and northern New Jersey. Careful exploration will probably discover a similar series 

 of hills, composed of unstratified upper till or of modified drift, at the border of the 

 glaciated area through Pennsylvania, Ohio, and states farther west. 



A later terminal moraine seems to be indicated by the line of drift hills which forms 

 the north shore of Long Island through the greater part of Brookhaven, Riverhead and 

 Southold. Its extension to the east appears to be through Plumb and Fisher's islands, 

 and the southern edge of Rhode Island ; thence to the Elizabeth islands, and from 

 them northward to Manomet hill. At this line the ice-sheet made a long halt in its 

 retreat. No similar series of drift deposits has been noticed farther north in New 

 England, over which the melting of the ice-fields seems in general to have been with- 

 out sufficient pauses for the formation of definite terminal moraines. 



It remains for us to inquire what was the origin, or mode of accumula- 

 tion, of the lenticular hills and slopes of till which have been found to be 

 abundant and prominent in many parts of southern New Hampshire. We 

 have seen that in Cheshire, Hillsborough, and Rockingham counties these 

 lenticular masses are scattered here and there, and in some places quite 

 thickly, upon three areas which vary from five to twenty miles in width, 

 and extend twenty-five or thirty miles from north to south, or from north- 

 east to south-west. The greater part of the most eastern of these areas 

 lies beyond the state line in Essex county, Mass. These tracts are sepa- 

 rated by others of equal or greater width, upon which scarcely any len- 

 ticular hills are found. This territorial division in three groups does not 

 appear to have been caused by differences in the adjacent stratified rocks; 

 it more probably resulted in some unexplained way from movements of 

 the ice-sheet. It is the only indication of system which we have discov- 

 ered in the distribution of these hills. Whether they occur rarely or very 

 abundantly, they are alike irregularly scattered without any apparent 

 order or connection, nowhere forming well defined series, like those of 

 the terminal moraines of Plymouth and Barnstable counties in Massa- 

 chusetts, and of Long Island and New Jersey. 



In Sullivan, Carroll, Belknap, Merrimack, and Strafford counties, len- 

 ticular accumulations of till are sprinkled more sparingly, with no traces 

 of system, being numerous in some localities, but generally rare or ab- 

 sent. With this diminution in numbers northward, the relative proper- 



