POST-TERTIARY PERIOD. 537 



while usually not exceeding a cubic foot in size, sometimes contain 

 a thousand cubic feet, and occasionally over twenty thousand. 



One boulder in Bradford, Mass., is 30 feet each way (Hitchcock), and Aveighs 

 not less than four and a half millions of pounds. Another, in Whitingham, in the 

 Green Mountains of Vermont, is forty-three feet long and thirty-two in average 

 width, and full 40,000 cubic feet in bulk. It lies on the top of a naked ledge. 

 Many on Cape Cod are twenty feet in diameter, and one at Winchester, X.IL, is 

 twenty-nine feet across. In the Lake Superior region, boulders of native copper 

 have been found. 



Drift icithovt marine fossils. — The Drift has afforded no proof by 

 means of shells or other marine relics that it is of marine origin. 

 It contains occasional pieces of wood, but nothing that can be 

 traced to the ocean or suggests that it was formed under salt 

 water. 



Arrangement of the material. — The material is coarsest to the north, 

 and becomes gravel and sand merely, without stones, towards the 

 southern limit of the Drift region. Nearing this limit, it stretches 

 somewhat farther south in the valleys than on the hills. 



Courses of Drift sometimes not conforming to the courses of existing slopes 

 or valleys. — The stones sometimes lie in long trains, as in Richmond, 

 Berkshire co., Mass., and Huntington, Vt., crossing hills and val- 

 leys, without following the line of slope ; or going obliquely across 

 a valley, as if the valley were neither an impediment nor guide to 

 the movement ; or the stones of one ridge are found on another 

 ridge separated from it by a deep valley. 



The great mass of gneiss at "Whitinghain, Vt., was probably transported 

 across Deerfield valley, the bottom of which is 500 feet below the spot 

 where it lies (Hitchcock). A block of granite nearly as large lies on Hoosac 

 Mountain, on the face overlooking a valley thirteen hundred feet below, — that 

 between Stamford and Adams, — which it had probably crossed. Such examples 

 are numerous. 



Source of the material. — The Drift (1) is derived from the rocks to 

 the north of where it now lies, mostly between northeast and north- 

 west ; in New England, mainly from the northwest, or between 

 north and northwest ; and (2) it has been transported to a distance 

 generally of twenty to forty miles, but sometimes also sixty or one 

 hundred miles. The distance is ascertained by comparing the rock 

 of the boulders with the rocks of the country. The granite, gneiss, 

 and syenite boulders of southern New England have been traced 

 to their original beds, somewhere northward of them. 



The iron-ore bed of Cumberland, Rhode Island, furnished boulders for the 

 country south to Providence, thirty-five miles, while none are found to the 

 northward. (Hitchcock.) 



