CURRENT PRE-CAMBRIAN LITERATURE 535 
Comments.—The use of the term Archean in two senses is objec- 
tionable. If it is used for all rocks older than the Cambrian, then 
another name should be applied to the basal complex. If, following 
the usage of the U. S. Geol. Survey, Archean is confined to the basal 
complex unconformably below the Algonkian, the general term for all 
rocks below the Cambrian should be pre-Camérian. 
- Clark describes the physical features and geology of Maryland, 
and gives a sketch of the development of knowledge concerning them. 
The description of pre-Cambrian geology Is essentially the same as 
that given by Clark in a preliminary publication of this part of the 
volume,? and this in turn is but slightly different from an account 
given by Williams and Clark in 1893. Both of these articles are 
reviewed above. However, a few minor changes may be noted. The 
crystalline rocks of the Piedmont Plateau region, instead of being 
divided into six types as before, are divided, into seven typesdiorite 
being added to the list. Rocks of the Archean period are placed 
in the table of formations as doubtfully present. 
Keyes gives a detailed petrographical description of the Maryland 
granites. For reasons the same as given by Williams they are regarded 
as eruptive, and many of the gneisses are shown to be dynamically 
metamorphosed granites. 
Darton‘ maps and describes the geology of the Fredericksburg 
sheet of Virginia and Maryland. He finds in the northwest and 
west parts that granite, gneiss, and schist occur, and in the northwest 
rWn. B. CLARK: Outline of present knowledge of the physical features of 
Maryland, embracing an account of the physiography, geology, and mineral 
resources; Maryland Geol. Survey, Vol. 1, Pt. III, 1897, pp. 139-228; Historical 
Sketch, Pt. II, zdzd., pp. 43-138. With map. 
2The physical features of Maryland, preliminary publication of Vol. 1, Pt. Il, 
1897. 
Geology and physical features of Maryland, by G. H. WitLiams and Wo. B. 
CLARK. Extract from World’s Fair Book on Maryland; Baltimore, 1893. 
3 Origin and Relations of Central Maryland Granites, by C. R. KEYEs, with an 
Introduction on the General Relations of the Granitic Rocks in the Middle Atlantic 
Piedmont Plateau, by G. H. WILLIAMS. Fifteenth Ann. Rep. U.S. Geol. Surv., 1895, 
pp. 685-740. Pls. XXXVI-XLVIII. 
4Geol. Atlas of the U.S., Fredericksburg Folio, No. 13, by N. H. DARTON: 
U. S. Geol. Surv., Washington, 1894. 
