REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1902 r31 



This rock forms the foundation for the city of Little Falls, and 

 the high terraces of bare rock [pi. 14-17] which extend east of 

 the city for more than a mile to the fault cliff. These upper 

 terraces have been produced by the cutting away of the Cal- 

 ciferous down to the basal crystalline; while the lower terraces 

 [see pi. 18-25] have been made by the trenching of the crystalline 

 rock by the Iromohawk (Iroquois-Mohawk) and the Mohawk 

 rivers. 



The upper terraces, representing the top of the crystallines, 

 dip rather steeply to the southwest, like all the strata at that 

 point, and in consequence the rock terrace on the north side of 

 the river is about 100 feet higher than on the south side. For 

 the same reason, the top of the crystallines is higher at the 

 crest of the fault scarp than westward at the city, and west 

 of the city it disappears under the Calciferous. The lower 

 benches, which are product of river erosion, slope east or down 

 stream. These relations of the rocks are shown in the plates. 



The rear boundary of the north terrace, or the base of the 

 Calciferous, is practically the 600 foot contour [see pi. 13]. On 

 the south side the corresponding terrace is about the 500 foot 

 contour. A road follows along the back of each terrace. So 

 much for the structure and present form. Let us now translate 

 the history. 



History 



It was suggested by Chamberlin that before the Glacial period 

 there existed here at Little Falls a divide between Hudson and 

 St Lawrence waters. Brigham has shown that probably the 

 rock bottom of the valley, beneath the filling of drift and 

 alluvium, slopes northwestward (up the present valley) to Rome. 

 We may reasonably assume that the hard rocks at Little Falls 

 formed an ancient col in the preglacial valley, and that the 

 waters flowed away from this point in opposite directions. The 

 form or hight of this col we do not know; but we may be sure 

 that it was unlike its present form. It is possible that some 

 Calciferous was in place on the Archean crystallines, and possi- 

 bly the latter were not exposed at all. It is also probable that 

 the glacier left some drift in this section of the valley. The 

 form and dimensions of the valley, with its position and rela- 



