Review of Recent Geological Literature. 411 
is much more fruitful than that which consists in distinguishing more 
than a hundred species of Unio in the waters of France, or in making, 
unwittingly, several species from two branches of the same plant." 
The entire work is established on a perfect sympathy with evolution. 
He refers frequently to American Neo-Lamarckianssuch as Hyatt, Cope, 
Riley, Marsh, and others of what he calls the American school. 
The volume contains numerous figures, many of them new. It com- 
prises the science in its present aspect, in the light of the latest research. 
It is an important and welcome addition to the literature of geology in 
the nineteenth century, and will constitute one of its noteworthy 
steps of advance. 
Finite Homogeneous Strain, FUnv, and Rupture of Rocks. By George 
F. Becker. Bulletin of the Geological Society of America, vol. iv, pp. 
13-90, with 23 figures in the text; Jan. 3, 1893. From experiments and 
elaborate mathematical investigation, the author explains the flow, 
shear, and faulting of rocks, and the origin of joints, schistose, and slaty 
cleavage, and basaltic columns. The columnar structure is attributed, 
as by former writers, to rupture by tension in the process of cooling and 
contraction. Joints are referred to simple unrotational pressure, which 
produces two sets of fissures crossing each other at angles approaching 90^' 
if the rock is brittle, but gives when the rock is plastic two sets of schistose 
cleavages. "The line of force bisects the obtuse angles of the cracks 
or cleavages." The accepted theories of slaty cleavage are shown to be 
erroneous, and it is ascribed instead to rotational pressure, receiving 
no aid from the presence of mica scales or flattened particles of the rock 
mass. "The most important result of theinvestigation is that jointing, 
schistosity and slaty cleavage all imply relative movement, and are thus 
as truly erogenic as faults of notable throw. They may all be regarded 
as orogenically equivalent to distributed faults. The great number of 
joints and planes of slaty cleavage compensates for the minute move- 
ment on each, and the sum of their effects is probably at least as im- 
portant as that of the less numerous faults of sensible throw. In the 
light of this conclusion it appears that if one could reproduce the oro- 
genic history of the Sierra [Nevada] in a moderate interval of time on a 
model made to a scale of one mile to the inch, it would seem to yield to 
external and bodily forces much like a mass of lard of the same di- 
mensions." 
TJie Thickness of the Devonian and Silurian Rocks of Central NewYork. 
By Chari.es S. Prosser. Bulletin, G. S. A., vol. iv, pp. 91-118; Feb. 21, 
1893. Detailed sections are recorded for twelve deep wells in the south 
to north belt in central New York which includes Binghamton, Utica, 
Syracuse, and Waiertown. The thicknesses of the several formations in 
descending order, reaching down to the Archaean, are found as follows: 
Chemung (in part) and Portage, 22.50 feet; Hamilton, 1785; Marcellus 
shale, 100(?); Upper Helderberg (Corniferous limestone), 93; Oriskany 
sandstone (?); Lower Helderberg, 186 (?); Onondaga Salt group, 1239-|-; 
Niagara, 52 (?); Clinton, 323; Medina, 520; Oswego sandstone, 107; Lor- 
