534 6. i, LIB IIVE 
rocks pegmatites are abundant. Some of these are, as indicated by 
their association with quartz veins and by parallel banding, water 
segregations. The majority, however, are igneous, as is shown by all 
of the phenomena of intrusive rocks. 
Comments—TVhe description and discussion of the origin of the 
pegmatites are of great interest. From the descriptions it is clear, 
although Dr. Williams does not definitely say so, that there are nearly 
all gradations from material which is plainly a vein quartz deposit, 
through others where we have quartz and feldspar with a banded 
arrangement, and are water segregations, to the pegmatites which have 
distinct igneous characteristics. This region thus affords a beautiful 
illustration of Van Hise’s’ conclusion that under proper conditions 
water and liquid rock are miscible in all proportions, and that pegma- 
tization comprises water impregnation, true igneous injection, and all 
intermediate processes. 
Clark‘ describes the geology and physical features of Maryland. 
This account is essentially the same as that published by Williams and 
Clark? in 1893, and previously reviewed. Here, however, the crystal- 
line rocks are classed as Archean and Algonkian, both of which are 
included under the general term Archean. ‘The statement is made 
that there is no positive evidence that there are represented in Mary- 
land rocks of the earliest portion of Archean time (meaning Archean 
proper), although a part of the gneiss complex may represent it. The 
Algonkian period, however, is represented by many varieties of rock. 
The rapidity with which the crystalline rocks furnished sediments for 
the overlying formations points to their high elevation in Archean 
time. 
In the western division of the Piedmont Plateau region of Mary- 
land, Algonkian rocks are present infolded with the Paleozoic deposits 
of Montgomery, Frederick, and Carroll counties. They consist of a 
single type resembling the metamorphosed basic volcanic rocks 
(Catoctin schist) of the Blue Ridge district. 
«Principles of North American pre-Cambrian geology, by C. R. VAN HISE: 
16th Ann. Rept. U. S. Geol. Surv., 1894-5 pp. 686-688. 
2 The physical features of Maryland, including the physiography, geology, and 
mineral resources, by WM. B. CLARK: Maryland Geol. Survey, preliminary publica- 
tion of Vol. 1, Pt. III, 1897, pp. 95. With map. 
3Geology and Physical Features of Maryland, by G. H. WILLIAMS and Wo. B. 
CLARK. Extract from World’s Fair Book on Maryland; Baltimore, 1893. 
