G. H. Williams—Norites of the “ Cortlandt Series.” 137 
Non-Curysouitic Rocks. 
Class Il. orite. (Esmark). 
The application of the microscope and accurate optical 
methods have been instrumental in showing that many rocks 
formerly supposed to contain orthorhombic pyroxene are in 
reality devoid of this mineral. Many of the so-called “ hypers- 
thenites” of the older petrographers contain only a glistening, 
bronzy diallage (the “diallage metalloide” of Hauy). This 
peculiar luster is found to be in no way connected with an 
orthorhombic crystallization, and yet the microscopic studies of 
rocks have by no means tended, to show that hypersthene is a 
less widely distributed mineral than was formerly supposed. On 
the contrary, orthorhombic pyroxene is constantly being found 
to be a more and more important rock. constituent. Not only 
is it discovered to have an unsuspectedly wide spread occur- 
rence in the younger volcanic lavas, but in the more basic of 
the older granular rocks true hypersthene is by no means a rare 
constituent. The localities for hypersthene-gabbro or hyperite 
are constantly increasing, wherever the older rocks are being 
studied. 
Hypersthene rocks have long been known to be developed 
on an enormous scale in the Laurentian formation of Canada 
and northern New York, where they are called anorthosite or 
norite. True hypersthene is also known to have a wide distri- 
‘ bution in the dark, fine grained gabbros of Maryland,* Del- 
awaret+ and Pennsylvania. These rocks are members of the 
Archean formation and resemble traps, although they are 
wholly different from the mesozoic diabase of the Atlantic 
border. 
The occurrence of a considerable area of massive rocks in 
which hypersthene is the prevailing bisilicate, on the southern 
flank of the Archzean Highlands of New York, is very interest- 
ing in connection with the distribution of this mineral in the 
rocks of the Appalachian belt to the north and south of it. 
The earliest identification of hvpersthene in the Cortlandt 
rocks is, as far as I have been able to ascertain, that of Hermann 
_Credner in 1865.t These rocks are described by Mather, in 
* See Bull. U. S. Geol. Survey, No. 28, p. 18. 
_ 4+. D. Chester: Proc. Acad. Nat. Sci. Philadelphia, Oct. 14, 1884. Dr. Geo. 
W. Hawes also found hypersthene-gabbros abundant in the White Mts., N. H. 
¢ It may be of interest to quote here a few sentences from Credner’s description of 
these rocks, given in an article entitled ‘‘Geognostische Skizze der Umgegend von 
New York.” He says: ‘‘ Noch einige Meilen (von New York) nérdlich wird der 
Gneiss sehr reich an Hornblende. bis diese den Glimmer noch und noch verdrazet, 
wodurch ein ausgezeichneter Hornblendeschiefer entsteht, welcher allmahlig sein 
schiefriges Gefiige verliert und zu einem porphyrartigen Syenit wird, in dessen 
weisser Grundmasse grosse blattrige Hornblendeindividuen ausgeschieden liegen. 
Von diesem Gestein sollen wiederum Uebergangsstufen nach dem Hypersthenfels 
