816 The American Naturalist. [September, 
* In view of present activity in the discussions of the antiquity of 
man, I can but regard. this publication of Mr. Diller as of the very 
highest importance as calculated to allay the fears of a certain portion 
of the Christian public, and to check the hasty inferences that some are 
likely to draw from the recent facts which have been so freely pub- 
lished concerning the relation of man to the lava beds of the Pacific 
Coast. The time has not yet come to give the full chronological sig- 
nificance to those facts.” 
J Continental Problems.—The annual address of Mr. G. K. Gil- 
bert, President of the Geological Society of America, consisted of a 
statement of six unsolved continental problems, with a discussion of 
each question in turn. (1) “ How are Continents supported?” intro- 
duced the doctrine of Rigidity versus Isostasy, with the weight of 
evidence in favor of the latter doctrine. (2) “ Does heat or composi- 
tion determine the difference in density of the material of the earth’s 
crust?” was discussed in connection with (3) * What caused the 
Continental Plateau?” in which the author spoke at length of the 
only hypothesis yet advanced, that of Mr. Dana, which deserves 
to be more fully compared with the body of modern data. (4) * Why 
do Continental Areas rise and fall?" is a problem for which no solu- 
tion has been suggested. (5) "Are Continents Permanent?" may 
probably be answered in the affirmative, but the fact is not yet fully 
established. (6) .* Do Continents Grow?” is still open to discussion, 
although the doctrine has been generally accepted. In the author's 
opinion, the greater part of the data from which continental growth 
has been inferred may be fictitious and up (Bull. Geol. Soc. 
Am., Vol. IV, 1893.) 
Mineral Resources of the United States for 1891.'— This vol- 
ume is the eighth of a series begun in 1882. It deals with the mineral 
progress of the year 1891, and contains a complete statement of the 
mineral products of that year. The opening chapter is a summary of 
the quantity and value of the metallic and non-metallic products for 
1891, and also contains tabular statements of the outputs from 1880 to 
1891. Under the head of Iron Ores, a résumé of the progress in the 
manufacture of iron and steel in the United States for the past twenty 
years is given. 
The names of the contributors of the various sections appear in con- 
nection with the subjects treated. 
1 Mineral Resources of the United States for the Calendar Year 1891. David S. 
Day, Chief of Division of Mining Statistics and Technology. Washington, 1893. 
