GEOLOGY OP THE VICINITY OF LITTLE PALLS 



69 



the rocks included are all that are now represented in the imme- 

 diate district, and the diagram is just as suitable for illustrative 

 purposes as if the higher rocks were added. As the district be- 

 came a land area, streams would extend themselves across it and 

 commence to wear out valleys, tributaries would develop to these 

 main streams, the topography would become more irregular be- 

 cause of this wear, and the precise sort of irregularity developed 

 depended on certain special characteristics of the district. These 

 were the original south slope of the surface, the gentle inclination 

 of the rocks, the variation in resistance of the different formations, 

 and the fact that the Paleozoic cover was thinner at the north than 



Pig. 13 Diagram to illustrate the condition of the region after deposition of the 

 Paleozoic rocks and emergence above sea level, with smooth, southerly sloping surface 

 B=Beekmantown, T=Trenton, U=Utica and Hudson shales and M=the Oswego anu 

 Medina sandstone formations of the Upper Silurian. 



Fig. 14 Diagram to illustrate the topography produced as a result of prolonged 

 erosion on the district shown in figure 13. The erosion stage represented is that of 

 greatest possible relief. 



at the south. In figure 14 an attempt is made to indicate the 

 character of the surface produced at a certain stage of the erosive 

 process. The Medina is the most resistant of the Paleozoic rocks 

 included, followed in order by the Beekmantown, Trenton and 

 Utica. The Medina would be first cut through by the streams at 

 the north because of its higher altitude there. Once the softer 

 rocks beneath were exposed, erosion would proceed more rapidly. 

 The pre-Cambrian rocks would be first uncovered on the north, 

 both because of higher altitude and because the Paleozoic cover 

 was thinnest there. This slow removal of the Paleozoic cover 

 would then advance southward. The successive Paleozoic forma- 

 tions would then be found infacing toward the old surface on 

 which they were originally deposited. The harder and more re- 

 sistent layers would iriface as lines of cliff, or escarpment, running 



