696 WOOD WORTH AND MARBUT 



in which bowlders are scattered as if they had rolled out of a 

 vanished cliff on the north. These fragments vary greatly in 

 size. Their general appearance is shown in Fig. 3, a view taken 

 from the crest of Cat Rocks. 



Bowlder Couplets. — Within this fringe and particularly near 

 the line where the materials begin to exhibit superposition, 

 instances may be observed where bowlders occur in pairs : a 



• <cd:-;.<]\ 



Fig. 4. — Bowlder Couplets. A, the stop ; B, the stopped bowlder. The arrow 

 indicates the direction of movement. 



firmly settled bowlder has one leaning against it on the northern 

 side, as indicated in the accompanying diagram (Fig. 4). These 

 couplets appear best explained by supposing that the leaning 

 bowlder tumbled outward from the ice and was stopped by 

 coming into contact with the block on the south which had 

 preceded it. The association of these colliding couplets with 

 the scattered bowlders above described suggests the probability 

 that the fringe as a whole is due to the falling out of bowlders 

 from the ice front. 



The structure of the Ttiam wall. — The belt at Cat Rocks is 

 accumulated on a slope, so that while the crest is upwards of 

 thirty feet above the frontal fringe by the roadside on the south, 

 the elevation of the inner mural margin is not more than from 

 three to six feet. The thickness of the belt, however, in places 

 must be from ten to fifteen feet or even more, for the bottoms 

 of the holes between 'the larger bowlders have not yet been 

 reached with certainty. Many of these spaces are so large as 

 to permit of the entrance of three or four persons with a little 

 inconvenience. The absence of fine materials in the belt is very 

 conspicuous. Although many trees are seen growing up out of 

 the belt, most of them are probably growing out of a soil 



