122 G. K. GILBERT — GLACIAL SCULPTURE IN WESTERN NEW YORK 



essentially a moutonnee surface, the bosses of which are measured hori- 

 zontally by miles and vertically by hundreds of feet. 



While the glacial sculpture of this district is probably as profound as 

 in tlie district described by Goodchild, the indicated work is less, be- 

 cause the softer rock offered less resistance, and in northern New York, 

 where the rocks are comparable in hardness with those of the Scottish 

 district, the ice seems to have accomplished comparatively little. Sand- 

 stones and limestones are not there so disposed as to afford good com- 

 parative data; but in a tract of crystalline schists lying northeast of 

 Carthage, and nearly bare of drift, the sculpture features are very differ- 

 ent from those depicted by Goodchild. The principal structure of the 

 schist is vertical, and its trend makes wide angles with the direction of 

 ice motion. The ridges, which are at most only a few scores of feet in 

 height, conform in trend with the strike of the foliation, and have been 

 but slightly remodeled by sculpture on lines of ice motion. The bosses 

 of the moutonnee pattern are measured by yards or rods. 



While these observations tell of ice action much less energetic than in 

 Goodchild's Scottish field, they do not conflict with his conclusions, but 

 merely show that local conditions were different. Whatever the general 

 potency of glacial ice, a wide variation of local power should be assumed, 

 and the extent to which ice is responsible for the topography of a dis- 

 trict is ordinarily a ])roblem to be solved onh^ through the study of local 

 phenomena. The question of the origin of the basins of the Laurentian 

 lakes and of the share of work borne by ice is, in my judgment, b}^ no 

 means insoluble, but will yield eventually to the careful accumulation 

 and scrutiny of available facts. The present paper, while avoiding the 

 general discussion, presents a body of facts which it is hoped may con- 

 tribute to the observational basis of the ultimate discussion. 



During the summer of 1898 ni}^ field work as a member of the United 

 States Geological Survey consisted in the detailed mapping of a district 

 along the shore of lake Ontario in New York extending from the Niagara 

 river eastward about 30 miles to the eastern boundary of Niagara count}'. 

 Reconnaissances had previously covered Orleans and Monroe counties, 

 so that some of the conclusions reached in the district of detailed work 

 could be extended with fair approximation from the Niagara river to 

 the Genesee. 



Observations on glacial sculpture pertained to the Niagara limestone, 

 the ledges at the base of the Niagara escarpment, and the INIedina shale. 



Sculpture of the Niagara Limestone 



In western New York the strata incline gentl}' toward the south, the 

 rate varying usually between 25 and 50 feet to the mile, but the general 



