The American Geologist. January, 1905 
regions of California; in Placer, Nevada, Yuba, Sierra, Plumas, 
and Butte counties; made in 1879." Appendix A, pp. 379- 
487, of "The auriferous gravels of the Sierra Nevada of Cali- 
fornia," Vol. 1, "Contributions to American geology," by J. D. 
Whitney, Harvard College, Museum of Comparative Zoology, 
Memoirs, Vol. 6, Cambridge, 1880. 
PRESENT PROBLEMS OF GEOPHYSICS.* 
By GEOR(iE F. Becker, Washington, D. C. 
Advances in science are seldom made without a view to 
the solution of specific, concrete problems, even when the 
results of investigation possess the widest generality. The 
history of science is full of instances of the fruitfulness of 
researches the immediate purposes of which were narrowly 
defined. Geophysics is only that portion of general physics, 
including under that term physical chemistry, which is applic- 
able to the elucidation of the past history and present condi- 
tion of the earth. It is thus a very definite branch of applied 
science, the exigencies of which call for the solution of a 
group of related problems. These, however, possess great 
interest apart from their application to the globe, while for 
the most part they offer very serious experimental and theo- 
retical difficulties. Had they been easy, they might have 
been solved long ago, for many of these problems have been 
propounded and more or less discussed from the birth of 
modern science to the present day. Their difficulty, not 
lack of recognition of their importance, has postponed their 
solution. 
The main purpose of this paper is to deal with the order 
in which it would be expedient to investigate the questions 
embraced under the head of geophysics, but a brief and 
incom])lete enumeration of the problems from a geological 
standpoint will serve to lend a coherency and a human in- 
terest to the subject which it would otherwise lack. 
Physical geology begins with the solar nebula and the 
genesis of the earth-moon system. The harmonies of the 
*Address delivered at the International Congress of Arts and Sci- 
ence, at St. Louis, before the Geophysical Section of Department 12, on 
September 21, 1904. 
