DISTRIBUTION OF THE GABBROS. 215 



all those mentioned from the oldest to and including the Utica. They 

 are not of stratigraphic moment, although of interesting petrographic 

 characters.* 



The great metamorphism of the region occurred before the deposition 

 of the Potsdam, and beyond question in pre-Cambrian times great geo- 

 logic forces of this nature operated ; but all the Paleozoic sediments 

 have suffered faulting and, as Brainerd and Seely have shown by careful 

 work in several districts, especially in Vermont, this is quite extended. 

 The same is generally true of the New York shore, although in less 

 degree. As the Green mountain axis is left behind, these post-Ordovician 

 upheavals and overthrusts are less marked. 



Distribution of the Gabbros. 



On the south the gabbroitic rocks are found in the western part of 

 Ticonderoga township as basic members, but unless some doubtful 

 gneisses represent them, they are not in large amount. In northwestern 

 Crown Point township and southwestern Moriah a great ridge offsets to 

 the eastward from the interior mountains and forms an enormous mass 

 in Moose mountain, Harris mountain and others. Anorthosites are 

 chiefly present, with some basic developments, around bodies of titanifer- 

 ous magnetite on Moose mountain. In ^loriah there are various outhers 

 of basic gabbro, but most interesting of all is the exposure along the 

 Delaware and Hudson railway track for three miles above Port Henry. 

 The cuts show dark green walls of this igneous rock, with interesting 

 contacts against crystalline limestone. They afford both normal and 

 olivine gabbro and most interesting passages into gneissoid facies and 

 developments of reaction rims around the basic minerals. All the 

 northern portion of \\'estpoi't is formed of the gabbroitic rocks, mostly 

 anorthosites, and in the ridge of Split Rock mountain they extend for 

 some miles along the lake shore. Western Essex, including Boquet 

 mountain, consists entirely of the same rock, and Trembleau mountain, 

 running through Chesterfield township, merely repeats Split Rock. 



Facies and mineralogic Composition of the Anorthosites. 



In these exposures we find chiefly coarsely crystalline, at times 

 gneissoid facies which contain much more labradorite feldspar than any 

 other mineral. Such are here called anorthosites, following the precedent 

 of Dr F. D. Adams,t and by the term, which in these regions is a practi- 



*See Bulletin 107, U. S. Geol. Survey. 



t F. D. Adams : Uber das Norian oder Ober-Laurentiau von Canada. Neues Jahrbuch, Beil. Band 

 viii, p. 423. 



