224 
GEOLOGY OF THE FOURTH DISTRICT, 
Upper and Middle Falls of Portage. From a sketch by Mrs. Hall. 
27. PORTAGE OR NUNDA GROUP. 
Sherburne flagstones and shale, Cashaqua shale, Gardeau and Portage groups, of the 
Annual Reports. 
(Part of No. 9, Pennsylvania Survey.) 
[See P of woodcut, page 27, and section of Genesee river, PI. XIII j also section of Lake Erie shore, PI. VII.] 
This group presents an extensive development of shale, shales and flagstones, and finally 
some thick-bedded sandstone towards its 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 general similarity, and from the difficulty also of separating it 
from the higher rocks on its southern limits, it is colored the same tint on the map, being the 
northern part of the light umber tint. 
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. 
