Recent Publications. 389 
the object being to ascertain whether or not they yield support to the 
theory of isostasy. This theory of course requires less gravitational ef- 
fect on sea-level in an elevated region than in one lying lower, in conse- 
quence of the loss of the positive and the presence of the negative 
attractive action of the elevated mass, the earth's whole surface being 
assumed by the theory to be in gravitational equilibrium, an assumjj- 
tion which may, however, be equally true on the theor\- of rigidit\". 
At eleven stations from Ithaca, N. Y., to Denver, Colo., the gravita- 
tional co-efflcient was found to average 980.151 dynes, the small varia- 
tions from this mean (which was obtained at Ithaca) showing no rela- 
tion to the altitude of the station. On reaching the mountains, how- 
ever, the reduced figures show at once a high excess above the average 
for the plain, being at Pike's peak 980.229 dynes. The isostatic theory' 
requires that they be less. The same is true in a less degree at all the 
mountain stations to Salt Lake Citj' exclusive, except at Grand Junc- 
tion and Green River. Obviously these results give no support to the 
doctrine of isostasy, and Mr. Gilbert says, "Gravity exceeds the Lsostatic 
requirement by 2,300 or 2,200 rock-feet. The evident suggestion is that 
the whole Rocky Mountain plateau, regarded as a prominence on a 
broader plateau, is sustained by the rigidity of the lithosphere." "The 
group of stations in the Yellowstone park repeats the suggestion for the 
Rocky mountains (.)f Montana." The two stations on the Colorado 
plateau give ver}' discordant results. At Grand Junction, gravity was 
found to etiual 980.198 dynes, an excess of 0.047 dyne, while at Green 
River it was 980.130 dynes, a defect of 0.015 dyne, a difference of 
1,800 rock-feet, which is not at present explicable. The same ditliculty 
was encountered at Washington and Philadelphia. 
On the whole, Mr. Gilbert says that he inclines to the conclusion that 
the mountains are upheld by the rigidity of the lithosphere, but that 
the great interior plain is in a state of approximate isostatic equilib- 
rium. 
We may hope that the interest and vahu' of such observations will 
lead to their continuance. The argument must be cumulative when 
the total amounts are so small and the variations so discordant. At 
present we do not feel that the results tell with any force in favor of ei- 
ther thcorj' to the exclusion of the other. The unknown factors in the 
problem are important and thf danger of error is great. E. w'. c. 
RECENT PUBLICATIONS. 
/. Government and Jitufe lirports. 
Geol. Sur. of Georgia, Bull. No. 1. A preliminary rt*[)ort on the mar- 
bles of Georgia, S. W. McCallie. 92 pp., 10 pis., 2 maps, 1894. 
Geol. Sur. of Georgia. Administrative report of the State Geologist 
for the year ending Oct. 2:5, 1894. W. S. Yeates. 9 pp., 1894. 
