54 ANNALS NEW YORK ACADEMY OF SCIENCES 



rich the surrounding magma in certain constituents, such as alumina. 

 It will be recalled that the numerous small schist inclusions — at Crugers, 

 for example — are also distinctly altered, but often in exactly the opposite 

 direction, so that magnetite, corundum, biotite, etc., are developed. 



Only one inclusion of limestone was found, which was either over- 

 looked by Dana or else its position on his rough map is not accurate. It 

 occurs along the post-road a short distance above Montrose, and on the 

 north the contact with the green pyroxenite described above is visible. 

 It is about seven hundred feet wide and is a medium grained, thoroughly 

 crystallized patch of the white Inwood limestone. The wernerite schist 

 described above may be mentioned in this connection, since its characters 

 would indicate that it is a thoroughly worked-over inclusion of limestone. 



A single inclusion of a rock which appears to be undoubtedly a basal 

 Highland gneiss was found. It is located on the shore of Lent's Cove, 

 and it seems to be only about seventy feet wide and of a slightly greater 

 length. It is almost entirely feldspar, which is very strongly kaolinized, 

 but which seems to be albite. There are also streaks of chlorite in the 

 rock; and the whole has a decidedly gneissoid aspect. It could not be a 

 dike or a member of the Cortlandt Series ; it is probably a xenolith of an 

 ancient gneiss, although it might also be thought that the igneous rocks 

 are thin over this area and that this outcrop represents a projection of 

 the gneiss which underlies the series. 



Structural Geology 



There is little that might be called structural geology that has not been 

 already discussed. Jointing usually occurs in these rocks, but always in 

 moderate development. The weathering of the olivine pyroxenites has 

 been noticed above, and the only other features of note may be now 

 briefly considered. 



DYNAMIC METAMORPHISM 



The amount of shearing undergone by the Cortlandt Series is, as has 

 been shown, slight but constant. It appears to vary somewhat among 

 the different members. The granites, although they carry microcline, 

 show strain in general to a very small degree.- It is only occasionally that 

 the norites exhibit any trace of the mortar structure, bent plagioclase 

 lamella?, wavy extinction, and twisted biotite that characterize the most 

 metamorphosed types. In but one or two instances was any crushing 

 seen in the pyroxenites. 



In the diorites and gabbros, however, the case is different. The former 

 group, as remarked above, shows perceptibly more strain than is to be 



