STRATIGRAPHIC VALUE OF THE PORTAGE 



SANDSTONES 



BY D. D. LUTHER 



James Hall, in his Report on the survey of the fourth geological 

 district of New York, 1843, p. 24, thus described, under the cap- 

 tion " Portage or Nunda group ", the strata succeeding the Gen- 

 esee shales in the valley of the Genesee river: 



This group presents an extensive development of slate, shales 

 and flagstones, and finally, some thick bedded sandstones 

 toward the upper part. Like all the other mechanical deposits 

 of the system, as they appear in New York, it is extremely 

 variable in character at different and distant points. . . 

 From its superior development along the banks of the Genesee 

 river in the district formerly included in the town of Nunda, 

 now Portage, it has received that name to distinguish it from 

 the higher rocks, which possess some differences in lithological 

 characters, but a more striking dissimilarity in organic remains. 



On p. 226, he says : " On the Genesee river this group admits 

 of the several subdivisions shown in woodcut 97, which are, in 

 upward order 1) Cashaqua shale, 2) Gardeau shale and flag- 

 stones, 3) Portage sandstones." 



The footnote accompanying the woodcut says : "As we go east 

 from this point, however, there is a constant increase in are- 

 naceous matter, and in a westerly direction an increase of mud 

 or shale." 



The strata that compose the Portage group as thus defined 

 are exposed almost continuously in the sides of the deep canyon 

 of the Genesee river from near its opening into the wide valley 

 near Mt Morris, to the top of the cliffs on the south side of the 

 high railroad bridge at Portageville, a distance of 15 miles in 

 a direct line, and about 20 along the tortuous river channel. 

 The difference in elevation between these points is 680 feet, and 

 the dip adds 381 feet to the rock section; total thickness 1061 

 feet. 



