No. 6.] UPHAM — GEOLOGY OF NEW HAMPSHIRE. 325 



NOTES ON THE SURFACE GEOLOGY OF NEW 

 HAMPSHIRE. 



By Warren Upham. 



The followiDg notes on the Drift or Post-pliocene deposits of 

 New Hampshire, are based upon explorations made in 1875 and 

 1876 for the State geological survey. 



To explain the striae, till, or boulder-clay, and modified drift, 

 ■which are found in all northern countries, has been a most diffi- 

 cult task, about which some diversity of opinion still remains. 

 The surface geology of New Hampshire seems to require the 

 bold theory of Agassiz, that an ice-sheet swept over our territory 

 from the North. This continental glacier became sufficiently 

 deep to cover every mountain summit in the State. That it over- 

 topped Mount Washington has been recently discovered by Prof. 

 C. H. Hitchcock, State geologist, who has found transported 

 rocks, and shown that glacial drift or till underlies the angular 

 blocks at the summit. Its thickness farther to the north was so 

 much greater than in this latitude, that its immense weight 

 caused the ice to flow slowly outward. The direction of its cur- 

 rent in New England was between south and south-east. Its 

 terminal front in the United States coincided nearly with the 

 course of the Missouri and Ohio rivers, passing into the ocean 

 south of Long Island. Its greater extent east of the Missouri 

 resulted from the increased snow-fall of this side of the continent. 



The conditions which brought ou the severe climate of this 

 period have been the subject of much speculation and discussion. 

 Mr. James Croll, with much probability, refers the ice- sheet to 

 an astronomical cause, and claims to determine the date and 

 duration of the glacial period. He supposes that an ice-sheet 

 was produced several times about each pole, a glacial epoch in 

 the northern hemisphere being one of genial climate at the south 

 pole, in which the ice-sheet disappeared.* It is certain that the 

 ice was partially melted at times, and that it afterwards advanced, 

 covering the territory from which it had retreated ; but the long 

 period requisite for the formation of the ice-sheet, and the low 



* Croll's "Climate and Time,'' pp. 76-78, etc. 



