PENNSYLVANIA ANORTHOSITES 
33 
from the Canadian and Adirondack anorthosites to support his 
theory. The paper gave rise to a succession of articles by Cush¬ 
ing and Miller,both of whom took issue with Bowen on his 
interpretation of the Adirondack intrusives. Miller’s conclusions 
are best summed up in the paper entitled “Adirondack Anortho¬ 
site.” The essential points of discussion between Bowen and 
Miller are stated in a later section of this article, dealing with 
criteria bearing upon the question of the origin of the Pennsylvania 
occurrence. 
The Pennsylvania anorthosite tract is located in the eastern 
part of the state, near Honeybrook in Chester County. * It lies 
between (40° 00') and (40° 10') north latitude and between 
(75° 45') and (75° 55') west longitude. The area of anortho¬ 
site measures approximately six miles in length and three and 
one-half miles in width. 
The Honeybrook area falls within that portion of the Appalach¬ 
ian Highlands which is commonly known as the Piedmont Prov¬ 
ince, and which comprises the Piedmont uplands and the Triassic 
lowlands. The northern one-third of the Honeybrook quadrangle 
lies within the Triassic lowlands; the southern two-thirds within 
the Piedmont uplands. The Piedmont Province is composed of 
a series of dissected plateaux extending as a broad upland to the 
southeast of the Appalachian Mountains. The summits of these 
plateaux are the vestiges of successive peneplains which have 
been traced by Bascom throughout the Piedmont province. In 
the Honeybrook district the anorthosite area represents a re¬ 
markably well-defined, but small physiographic and lithologic 
unit. It is a dome-shaped upland, elliptical in outline, within 
which are found a few isolated remnants of the Honeybrook pene¬ 
plain at altitudes of about 700 feet. This clear-cut oval area of 
the anorthosite is surrounded by quartz-monzonite except on the 
south where a fault brings a Cambric quartzite series against 
the intrusives. 
The configuration of the surface in Late Cretacic time, when 
regional uplift renewed erosion on the Honeybrook peneplain, 
may be hypothetically reconstructed from the following interpre- 
29 Ibid., Vol. XXV, pp. 501-509, and 512-514, 1917. 
30 Bull. Geol. Soc. America, Vol. XXIX, pp. 399-462, 1918; also Bull. N. Y. State 
Mus., Nos. 211, 212, 213, 214, 1919; also Journal Geology, Vol. XXIX, pp. 29-47, 1921. 
31 Bull. Geol. Soc. America, Vol. XXIX, pp. 399-462, 1918. 
32 Journal Geology, Vol. XXIX, pp. 540-559, 1921. 
