Review of Recent Geological Literature. 12t^ 
study of the granite of Barre, Vermont, with a geological,' map of 
Orange count.v, with parts of contiguous counties. This map shows 
twenty-five isolated small areas of granite, the chief of which are in the 
geographic area of the Washington limestone, or marble. This lime- 
stone has been hitherto considered Upper Silurian, (Dana) but Dr. C 
H. Richardson, who contributes this chapter, shows by the discovery of 
fifteen species of fossils that it is of the age of the Lower Trenton. He 
also remaks that so far as Orange county is concerned there is no ap- 
pearance of non-conformity between the eastern slate (the bottom of 
the Trenton) and the western (the culmination of the period), but the 
succession is continuous from east to w^est. "If ever such relations are 
found between upper and lower Silurian terranes of eastern Vermont. I 
am confident that it will be in the vicinity of lake Memphremagog. 
Prof. Perkins gives a full description of the geology of Grand Isle, 
of the Chamnlain valley, on which is found a series of strata running 
from the Beekmantown to the Utica, accompanied by a geological map 
of the island. He was assisted by Prof. H. M. Seely who has rend.-red 
a discussion of the sponges of the Chazy formation, and H. W. Shimcr 
who has petrographically examifled the dikes of the island. n. h. w. 
Magnetic decUuatinn tables, ami isogotiit charts for ig02, and Princi- 
pal facts yclating to the Earth's magnetism. L. A. Bauer. U. S- 
Coast and Geodetic Survey. O. H. Tittm.\x. Superintendent. 
Washington, 1902. 
This valuable document should be in every geologist's library. The 
long series of magnetic observations conducted, or collected, by the 
United States Coast and Geodetic Survey, begins to bear fruit of high 
scientific value- Other publications of the survey have isogonic charts 
of equal magnetic declination, but this volume not only is a compend 
of all previous data and tables, but contains an instructive presentation 
of the progress of knowledge concerning the magnetism of the earth be- 
ginning with the the earliest mention of the magnet or lode.stone and 
its polarity, the discovery and improvements of the marinei-'s compass, 
the dipping action of the needle, the discovery of Gilbert in the six- 
teenth century that "the earth itself is a great magnet," the causes 
thereof, the declination of the luagnetic needle, the secular change of 
the magnetic declination discovered by Gellibrand in 1634. t^^c secular 
variation of dip and of intensity of the magnetic needle, the time in- 
tervals between extreme positions of the needle, the irregularities of the 
same, the general clock'mise direction of the secular variation of the north 
end of the needle, the diurnal variation of the magnetic declination, its va- 
riation with the sun-spot period (11 years), annual variation of the mag- 
netic declination, its cause or causes arc outside the earth, magnetic 
storms, their relation to solar activity, to earth's cataclysms, (earthquakes 
and volcanic outbursts) and to electric currents in the upper regions — 
these topics, and the ways and means of recording magnetic observa- 
tions., especially in the United States, and charts expressing the geo- 
graphic 7one> of variation, are lucidly I'resented by Dr. Bauer in an 
introductory chapter. The body of the volume is taken up with a record 
