Published monthly by The Agassiz Association, ArcAdiA; Sound Beach, Connecticut, 



Subscription, $1.00 a year Single copy, 10 cents 



Entered as Second-Class Matter June 12. 1909, at Sound Beach Post Office, under Act of March 3, 1897. 



Vol 



VIII 



DECEMBER 



Number 7 



BOULDERS 



By Professor William North Rice, Wesleyan University, Middletown, Connecticut 



Probably few readers of this paper 

 living in New England or in adjacent 

 parts of the United States and Canada, 

 have failed to notice the frequent occur- 

 rence of loose pieces of rock of difTerent 

 kinds varyingin size from cobble-stones 

 to masses many tons in weight. These 

 boulders are often found lying on the 

 surface of the ground. Sometimes a 

 boulder is perched upon a ledge of rock 

 very different from the boulder. Often- 

 times a boulder rests upon a very small 

 base, so as to suggest the idea that it 

 would be easy to rock it and even to 

 tip it over. Such boulders, in Burling- 

 ton, Connecticut, are shown in Figures 

 I and 2. Rarely a huge boulder is 

 found so nicely balanced that it actually 

 can be made to rock. While many of 

 these boulders lie upon the surface, 

 others are foimd beneath the surface, 

 buried in a mass of disintegrated rock 

 material in which coarse and fine stuff 

 are mixed helter-skelter. The smaller 

 boulders are often utilized for stone 

 walls. Thus the fields are cleared of an 

 incumbrance, and serviceable and pic- 

 turesque walls are provided at small 

 expense. Sometimes a boulder may be 



recognized as a fragment of some more 

 or less peculiar kind of rock of which 

 a ledge is known to occur at some dis- 

 tance from the present situation of the 

 boulder. In this part of the country, 

 when we can recognize the probable 

 source of a boulder, it is found that 

 the boulder has moved southward from 

 its original home, though the direction 

 of its movement may have been con- 

 siderably east or west of a meridian 

 line. While most readers can verify 

 most of these facts by their own obser- 

 vation, comparatively few have de- 

 finitely asked themselves the question, 

 what is the meaning of the facts. To 

 answer that question is the purpose of 

 this article. 



Wherever ledges of rock are exposed 

 to the atmosphere and to rain water 

 percolating downward through cracks 

 and crevices, the rocks tend to become 

 disintegrated. The process is partly 

 mechanical. Water freezes in the 

 cracks and so splits the rock. Changes 

 of temperature, between the blaze of 

 sunshine and the coldness of night, 

 produce alternate expansion and con- 

 traction which tend to shatter the rock 



Copyright 1915 by The Agassiz Association, ArcAdiA: Sound Beach, Conn. 



