Review of Recent Geological Literature. 189 
the "layer of no strain." Estimates published a few years ago when 
the topic was first discussed placed this stratum at a depth of about 
two miles below the surface. But it was pointed out at the time that 
so small a depth could not be sufficient, because many cases were known 
in which strata have been brought to the surface by folding from far 
greater depths. This is the case, for instance, in the Appalachians, 
where rocks that were once covered with eight miles of other beds are 
exposed to the day. 
Mr. Davison says, "Estimates of the depth of the surface of no strain 
have hitherto been founded on the assumptions that the conductivity 
and coefficient of dilatation are constant." But taking the other datum 
that these factors increase with the temperature and following out the 
calculation, Mr. Davison comes to the conclusion that with an initial 
temperature of 7.000'' and a period of 100,000,000 years the level of no 
strain would be at the depth of nearly 8 miles. Evidently, however, 
even this increased depth will fail to satisfy the physical geologist, as 
shown above. Mr. Davison, however, says, "The numerical results here 
obtained cannot be regarded as reliable. They are given for their qual- 
itative rather than their quantitative v'alue," and concludes thus, "If 
we regard the contraction theory as a theory of the formation of moun- 
tain ranges only and not necessarily of the continental masses, we 
naay. I think, conchide that calculations as to its alleged insufficiency 
are at present inadmissible." e. w. c. 
The Great Vallei/ of California : a Criticism of tlie Theory of Ison- 
tasy. By F. Leslie Ransome. (University of California, Bulletin of 
the Department of Geology, vol. i^ pp. 371-428, Berkeley, Cal.. May, 
189G. Price, 45 cents.) The valley plain of the Sacramento and San 
Joaquin rivers, with its continuation in the area of interior drainage 
tributary to Tulare lake, has a length of about 400 miles and an average 
width of 50 miles, giving it an area of 20,000 square miles. Excepting 
at San Francisco bay, this lowland plain is entirely enclosed by moun- 
tains, its eastern and western bovindaries being respectively the Sierra 
Nevada and Coast ranges. It dates from the time of great orogenic dis- 
turbance at the close of the Miocene period, by which the Coast ranges 
were first ufjlifted as a connected mountain chain ; but the principal 
topographic features may be said to have their origin in the long subse- 
quent Early Quaternary faulting and westward tilting of the Sierra 
Nevada belt, raising its eastern border to its present great hight, while 
at the same time the Coast mountains were again greatly uplifted. But 
these orogenic movements on both sides of the valley plain have been 
also continued, as the author affirms, during the Pleistocene period, 
with their antithesis in the progressive suljsidence of the intermediate 
valley belt, upon which Quaternary sediments from the waste of the 
mountains have i)een deposited to ama.vimum thickness exceeding 2,000 
feet. The relationship between the sedimentation and the subsidence 
is shown to be discordant with the theory of isosta.sy, as applied to such 
restricted areas of the earth's crust, though perhaps not opposed to its 
application to continents and ocean basins. w. u. 
