284 SURFACE GEOLOGY. 



nents average coarser. This hardpan is certainly prior in age to the 

 lower till ; but that circumstance may not compel us to call it Tertiary. 

 If length of time is requisite for the induration of till, this hardpan should 

 be much older than the common moraine. There is nothing of signifi- 

 cance in the shape of this earth heap. It is not as conspicuous as a 

 small lenticular hill. After the access of air to the lower deposit, its 

 great induration disappears. When it is well exposed to rain, water 

 mixes with it, making a compound that will flow readily down a slope. 



A case similar to this is in Pittsfield, midway between Webster's mill 

 and the village. The railroad excavators had the same experiences that 

 have been narrated for Lyndeborough. Gov. Prescott informs me that 

 similar experiences befell persons endeavoring to excavate the earth for 

 a well near his residence in Epping; and recently I found the same 

 story told of drift in Amherst, Mass., and Hartford, Conn. The exam- 

 ples may multiply, and eventually furnish us the answer to our question 

 as to the peculiarities of their origin. 



Drift in North Conway. 



As an example of the aspect of the difference between the ordinary 

 till and the modified drift, I would refer to the accompanying heliotype, 

 illustrative of these two deposits in North Conway where the road 

 crosses Artists' Falls brook, near the Macmillan hotel. To render the 

 sand more distinct, a faint brown color is employed to show its limits. 

 It is about 10 feet thick, forming about one fifth part of the exposure. 

 There are boulders in the till here about a yard in diameter. The sand 

 of North Conway is usually widespread, but very thin. Quite a large 

 mass of it, as long as a small lenticular moraine, occurs just to the south 

 of the stream opposite the hotel. This 4s the position from which the 

 fine view of Mt. Pequawket, employed for the frontispiece of Volume II, 

 was taken. 



Plant Relics op the Glacial Period. Full descriptions of the Hudson's Bay and Greenland floras 

 now existing in the White Mountains have been presented in Volume I, pp. 392 and 568. No better argument 

 to show that an arctic climate once existed in New Hampshire than the presence of these plants, as well as the 

 corresponding insects described in the same volume, Chapter XII, can be adduced. They also imply the cor- 

 rectness of the glacial instead of the iceberg theory of the drift, and also that the cold conditions spread them- 

 selves gradually over the continent, disappearing slowly also. 



