1893.] Recent Literature. 455 
RECENT LITERATURE. 
A Summary Description of the Geology of Pennsyl- 
vania. Vols. I and II.'—The results of the Geological Survey of 
Pennsylvania from its beginning, in June, 1874, to the close of its field 
work, June 1, 1890, have been summarized by Professor J. P. Lesley, in 
three octavo volumes of 700 to 800 pages each, of which Vols. I and 
II have just been issued, while Vol. III is promised in June, 1893. 
This summary is compiled from the reports published by the Board 
since 1875, with the corrections, and the additions that the accumula- 
tion of fresh facts make necessary. Vol. I describes the most ancient 
deposits: The Laurentian granites, gneisses and mica schists; the 
Cambrian gneisses, schists and limestones ; the lower Silurian lime- 
stones and iron ores, roofing slates and mountain sandrocks ; Forma- 
tions II, III and IV, in the order of advancing time and superposition. 
The second volume describes the Upper Silurian red shales, limestones, 
and fossil iron-ore beds; the glass sand-quarry rocks; the black and 
gray shales, and the gray and red sandstones, with fish beds; Forma- 
tions V, VI, VII, VIII and IX reaching to the top of the Catskill 
Mountain rocks, the upper limit of the Devonian system. 
Each formation is discussed in detail. Its geographical distribution, 
thickness, lithological characters and fossil contents are carefully 
described, together with its relation to similar formations of neighbor- 
ing states. 
The question of sedimentary Archean rocks receives attention, and 
while discussing Archean rocks in general, Professor Lesley calls atten- 
tion to the fact that the Huronian rocks of Canada are nowhere recog- 
nized along the Highland Belt from the Hudson to the Schuylkill. In 
the author’s opinion, the term Huronian, “ must be used simply as a 
proper and private name for a series of rocks exposed along that 
part of the northern boundary of the United States.” In the paleozoic 
series, Professor Lesley does not clearly discriminate between the Cam- 
brian and Ordovician limestones, including them all under the one 
head of No. II, as was done by the first geological survey. He leans 
toward the explanation given by Dr. Fraser of the structure of the 
Chester Valley, rather than those of Hall and Rogers. 
The illustrations are numerous, many of them being photo-electro- 
1 A Summary Description of the Geology of Pennsylvania. Final Report ordered 
by Legislature, 1891. Vols. I and II. By J. P. Lesley, Director, Harrisburg, 1892. 
