37 2 NEW YORK STATE MUSEUM 



In general for the whole Highlands region and southward^ 

 the lower group, nos. i and 2, Inwood and Manhattan, never 

 give evidence of great unconformity with the gneiss. The for- 

 mations are contorted in an exceedingly complex manner, are 

 always thoroughly recrystallized, follow the general foldings of 

 the lower gneiss and are abundantly injected especially by the 

 pegmatites and basaltic or diabasic intrusions and rarely by 

 granites in similar manner to the gneiss. But the group is not 

 always in contact with the same members of the gneiss series. 

 For example, only a few of the many outcrops of crystalline 

 limestone exhibit a contact with the quartzite referred to as 

 the Lowerre and which it is supposed to succeed. The contacts 

 are quite as likely to be with the banded gneiss or massive gran- 

 itic gneiss or even granite and schist. Of course, much of this 

 may be due to flowage in connection with the close folding and 

 metamorphism to which the whole series has been subjected. 

 But this common observation together with the fact that the 

 gneiss is much more complexly injected with igneous types and 

 contains an amount of such matter greatly exceeding that found 

 in the overlying group and also types not found in them at all„ 

 leads to the conclusion that there is not a perfect conformity 

 with the basal gneiss. It probably represents an overlap type 

 of sedimentary contact. 



Number 3, and therefore the whole group 3, 4, 5, is always 

 clearly unconformable on the gneiss where its true relation can 

 be determined. It lies on the upturned and eroded edges of 

 the folds of the basal gneisses. No part of this series is intruded 

 or cut by igneous masses or injected with pegmatites or in 

 any way complicated by the igneous associations so character- 

 istic of the older formations, except by the Cortlandt series. 

 That igneous mass, however, has such a distinct isolation from 

 the other igneous types that it may readily be dealt with as 

 an exception. 



This upper group is sometimes not disturbed, as for example 

 along some parts of the northern border of the Highlands, south 

 of Johnsville village and Shenandoah, where the unconformity 

 is beautifully shown and where it may be seen to have taken 

 no part whatever in the metamorphic foldings of the gneiss. 

 This upper group as developed along the northern margin just 

 described is known to be of Cambro-Siluric age. Fossils are 

 not plentiful but have been found at several localities ; Cambric 



