^Review of ''Recent Geological Luerature. 129 
author on The Organic Origin of the Chert, noticed in the February 
Geologist, page 121. A specimen of chert, forwarded to Dr. Hinde by 
Prof. G.Lindstrdm of Stockholm and collected from Permo-Carbonifer- 
ous strata of Spitzbergen, was found on examination with a hand-lens to 
be almost entiiely composed of spicules of sponges irregularly inter- 
mingled. The geological horizon of the beds furnishing the chert in 
Spitzbergen is nearly the same as that at which the spicule-bearing 
chert of Ireland and Yorkshire was obtained. Indeed, according to Hinde, 
the Spitzbergen beds "form the upper portion of a series of rocks regarded 
stratigraphically as the equivalents of the Carboniferous Limestone, 
even though the}' contain a certain admixture of Permian fossils." 
American Geological Classification and Nomenclature. By Jules Marcou. 
Cambridge, Printed for the author. May, 188S. In this pamphlet of 75 
pages the author gives us a general discussion from his point of view of 
the classification and nomenclature of the geological systems, divisions, 
etc, of North America. Strong arguments are presented in favor of the 
claims of the Taconic System as a term to denote the rocks containing the 
first fauna. The pamphlet, however, is throughout so largely con- 
troversial, and discusses so many points of interest to geologists in gen- 
eral, that instead of giving what would necessarily be an unsatisfactory 
outline of the points treated, we refer readers of the "Geologist" to the 
pamphlet itself. 
Three fortJtations of the middle Atlantic slope. By W. J. McGee — 
(American Journal of Science Feb., April, May and June, 1888.) In 
these four papers which are now bound together and distributed by the 
author in pamphlet form we have the results of considerable work on 
some hitherto obscure formations developed in the middle portion of the 
Atlantic slope. 
The first to be described in the paper, and the first in geological se- 
quence, is the Potomac formation. Reference is made to this formation 
and to the Dinosaurian remains that have been obtained from it, in the 
Geologist for February, 188S. page 136. According to McGee the 
Potomac formation extends from Weldon, N. C, through the intervening 
region, into New Jersey. South of the Rappahannock it is exposed 
chiefly along the waterways, while to the north of the river mentioned 
the formation is exposed at the surface over considerable areas, appear- 
ing extensively in railway' cuttings or capping eminences of circumdenu- 
dation. 
One of the chief points of interest in connection with the Potomac 
formation is the fact that it helps to supply some of the hitherto missing 
portions of the geological record. One instance must serve as an ex- 
ample. The great break that has heretofore existed in tiie history of the 
development of our forest flora is now partially filled up. Cycads and 
conifers were the predominant types in the early Mesozoic forests. But 
cycads and conifers are pre-eminently archaic types, connected by means 
of a more or less perfect series of gradational forms with the earliest 
terrestrial flora. In the Cretaceous forests we have poplar, sassafras, 
