STKATir.RAVITir VALI'E OF THE POUTACJE 

 SANDSTONES 



BY D. I). LUTIIEU 



James Hall, in his 7?f7>or/ o// the survey of the fourth geological 

 district of Xeir York, 184:^, \k l'4, thus described, under the ca]>- 

 tion " Portajic^ or Nnnda j^ronp ", tlie strata snceeedinji: tlie (leii- 

 esee shales in tlie valley of the (leneseo river: 



This j^rou]) ]>resents an extensive di'velopnient of slate, shales 

 and lhi;istones, and tinally, some thiek bedded sandstones 

 toward the njiper jiart. Like all the other mechanical deposits 

 of the system, as they ai>i»ear in New York, it is extremely 

 variable in chara<ter at different and distant ])oints. . . 

 From its superior develojunent alonj:: the banks of the (Jenesee 

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

 now Portajje, it has received that name to distinjfuish it from 

 the hi^'her rocks, which possess some differences in litholoji:ical 

 characters, luit a more striking dissimilarity in orj^anic remains. 



On p. 220, he says: '' On the Genesee river this j:roup admits 

 of the several subilivisions shown in woodcut !)7, which are, in 

 upward order 1) Cashaqua shah', 2) (lardjaii shale and flap: 

 stones, :*>) l*ortajjje sandstones." 



The footnote accompanying the woodcut says: 'As n\«- j;«> rast 

 from this i»oint, however, there is a constant increase in are- 

 naceous maltei', and in a westeily directiou an increase of imid 

 or shale." 



The strata thai c(uiipos<' the I'ortaj'c <;roup as thus defined 

 are exposed almost continuously in the sides of the deej) canyon 

 of the (Jenesee river from neai- lis openin*? into the wide valley 

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

 hij^h railroad bridf^e at T*ortaf^eville, a distance of 1.") miles in 

 a din'ct line, and about 2(1 along the tortuous river channel. 

 The difTerenr< in elevation between these points is tISO feet, and 

 tlie di|» adds .*!S1 f<«( in ijir incK s('( linn: lotal tliirkness 1001 

 feet. 



