80 G. H. SQUIER 



weathered portions they often project nearly their entire diam- 

 eters. 



It is evident that the resistance of the sand grains to abrasion 

 was greater than the strength of the cementation, so that the 

 abrading agent removed them integrally instead of wearing them 

 down to a common surface. There is, however, near one edge 

 of the facet a small concretionary nodule within which the great 

 abundance of iron furnishes a strong cement. In this the indi- 

 vidual grains are worn to a common surface, the effect being 

 equal to the best examples of glacial polish. A portion of this 

 concretion passes over onto the weathered surface where the 

 grains are all entire, and owing to the strong cementation many 

 of them are held as the capping of little pedicels, giving a very 

 rough surface. The bedding plane of the bowlder is parallel to 

 its longer diameters, and the flattened facet is nearly perpendic- 

 ular to this. The facet is crossed in a direction perpendicular 

 to the bedding plane by a straight groove about % in. wide and 

 deep enough to render it perfectly distinct. Other markings 

 are but faintly shown, but so far as they are distinguishable they 

 are parallel to the groove. 



It appears quite evident that this abraded facet was super- 

 imposed on an originally weathered surface, for sundry depres- 

 sions occurring within itwere not affected by the abrasion, but still 

 retain their original weathered character. Taking all these 

 features into consideration I think it may be said that they are 

 such as are characteristic of glacial abrasion, while it is hard to 

 suggest another agent by which they could have been produced. 

 Certainly none which we have the least reason to believe was 

 operative in the locality. 1 



I have mentioned that the bowlder lies at the bottom of a 

 ravine. It may therefore be well to add that although it is 

 exposed to the action of the occasional torrents, yet the facet 

 in question is turned away from them, while that portion which 



1 It would seem that abrasion of this kind and extent might be within the com- 

 petency of the friction to which ordinary talus is liable to be subjected in descending 

 a slope. — Ed. 



