HUDSON RIVER BEDS NEAR ALBANY 557 



lower I'laumans kill and in tlie Brothers's quarrj at South Troy, 

 probably are not merely contortions restricted to weaker strata, 

 for the heavy sandstone banks are also involved in the folding, 

 tout, probably, partake of the nature of smaller folds riding on 

 the larger ones, a phenomenon observable in many folded regions 

 and which, when regularly and strongly developed, has been 

 termed an anticlinorium by Dana. Viewed in this light these 

 narrow, but steep folds serve as additional evidence of the pres- 

 ence of a larger fold of a higher order.^ In fact it is necessary to 

 assume the presence of such riding folds of various sizes to ex- 

 plain certain irregularities in the succession of the beds within 

 the zones in this region. Thus it will be difficult to account in 

 any other way for the presence of the upper Utica beds on north- 

 ern and eastern Green Island, where we should expect the lowest 

 Utica beds. Also the apparent intercalation of shales with 

 X> i p 1 g r a p t u s a m p 1 e x i c a u 1 i iS in lower Dicellograptus 

 «hales, east of Mt Olympus, may, on farther investigation, find its 

 explanation in such minor folds. 



The end which the writer has in view in discussing the tectonic 

 relations of the investigated area is to demonstrate that the in- 

 verted position of the beds can be brought into harmony with the 

 general structure of the whole region, and that this inversion, 

 therefore, can not in any way be construed as weakening the con- 

 clusion drawn from the succession of the zones and the paleon- 

 tologic evidence, viz that the Normans kill or Dicellograptus zone 



^Tlie possibility tliat the whole region investigated is built up of nothing 

 but closely packed, overturned small folds, such as were found by Shaler 

 farther south (18) and are described by Dale (63) from the slate belt, has not 

 been discussed by the writer, though the presence of such small folds can 

 be observed in several localities; for, on account of their small size and evi- 

 dent surficial character, they would not be able to produce such long and 

 wide belts of rocks, as for instance that of the Utica shale. Dale 

 (63:199) also reports that in his territory, the northern extension of our 

 region, "series of such various folds form compound anticlines, and these 

 minor Cambrian anticlinoria alternate with Ordovician synclinoria con- 

 formably overlying Cambrian ones. As the Ordovician area consists of 

 shales, slates, grits and small quartzite beds, the beds being more hetero- 

 geneous, slaty cleavage is less prevalent, but the folds are also overturned 

 toward the west". 



