Review of Recent Geological Literature. 139 
is found, similar to the Cambrian limestone of Lena, but very poor of 
fossils. In it was found only one pigidium of a trilobite of the genus 
Dikelocephaluii. 
Perhaps, to this large Cambrian basin can be referred the stylolite 
limestone with Foramiuifera, developed in the Middle Toongooska, and 
the limestone of Torgoscha, which contains the trilobites, Proetus 
slatkoivski and Cyphaspis sibericus, as well as the corals that Mr. 
Toll described as forms of the genus Archecocyathus, for the first time 
found in the Cambrian of Canada and having a large extension in the 
Cambrian of Europe. Since in the Cambrian of European Russia only 
littoral deposits occur, the author thinks the most probable explana- 
tion of this fact is to suppose that these corals were migrating from 
the east. a. w. p. 
The ancient volcanic rocks of South Mountain. Pennsylvania. 
Florence Bascom. Bulletin No. 136, U. S. Geol. Survey, 1896. Oc- 
tavo, 124 pp., 28 plates of microscopic characters and geological map; 
15 cents. This work reviews previous descriptions of the igneous rocks 
of South mountain by the geologists of Pennsylvania, beginning as early 
as that of Lewis Evans, in 175.5, and ending with the last expressions by 
Hunt. Frazer and Lesley. By these geologists, without exception, these 
rocks were regarded as metamorphosed elastics. An exception might 
be made, as noted by Miss Bascom, of the sketch of J. F. Blendy. 1879, 
who referred to the greenstones as "amygdaloidal trap," and correlated 
the formation with the copper-bearing rocks of the lake Superior region. 
The acid rocks, however, he considered still as "slates."' 
It was in 1892 that appeared the first paper which advocated the ig- 
neous origin of these rocks, the result of field work done by the late Dr. 
Geo. H. Williams and by Miss Bascom. Since then the same geologists 
have fully demon striated, by more detailed examinations, not only the 
eruptive nature of these rocks, but also their probable extension along 
the Appalachian mountains, from Vermont to North Carolina. 
These volcanics are associated with certain sedimentary strata which, 
on the basis of some examination, Mr. Walcott has concluded are of pre- 
Cambrian age. The structural evidence of the prior date of the volca- 
nics is, however, not as convincing as is desirable. Dr. Williams, indeed, 
was led to express his doubt as to the volcanics being earlier than all of 
the sedimentary strata. They may be older than the Potsdam sand- 
stone, which is correctly classed, there, as Cambrian, but there is a 
much older and very important member of the Cambrian which exists 
below that quartzyte. 
The author's description of the three rock types is full and convincing, 
on all the questions on which she differs from the Pennsylvania geolo- 
gists. 
These three types are: 
"1. A siliceous sedimentary rock, represented by a quartzose con- 
glomerate, a sandstone and a quartzyte. This is rarely accompanied by 
an interbedded argillaceous slate. 
