Geolor/ical Society and A. A. A. S. Meetings. — (Jphatn. 243-* 
aom or never fovind naturally exposed on account of their more rapid 
absorption of heat. 
Burrowing animals, especially ants and termites, contribute much to 
the chemical agencies of rock decomposition. The soil of Brazil is fairly 
alive with these insects: their burrows penetrate to a depth of ten or 
twelve feet and radiate on all sides. Into these openings they carry 
plant food, and the acids from their decay and from the breath of the 
insects help to hasten the decay of the rocks below. ■ . 
Vegetation in the tropics is notoriously abundant and rank: the decay 
of so much organic matter in a hot and moist climate jjroduces large 
quantaties of humus acids that attack the rocks into which they are 
carried by the rains. The amount of carbonic acid carried to the earth 
is calculated from determinations of it in rain water and from the rain- 
fall in that country. Nitric acid, produced by electric discharges, falls 
in larger quantities in Brazil than in the temperate regions of the earth. 
The amount of acid to the litre of water has been determined from di- 
rect observations, and this with the rainfall furnishes the data for de- 
termining the total precipitation of nitric acid. 
The annual rain fall of Brazil ranges from about three feet at Rio de 
Janeiro to seven and a half feet at Manaus on the Amazon, and almost 
twelve feet on the mountain near Santos. This great precipitation is 
not distributed throughout the year as it is in temperate regions, but is 
concentrated for the most part within less than six months. The long 
dry season dries the ground out so that enormous cracks are opened in 
places to depths of ten or fifteen feet. Air circulates freely in these 
openings, and when the rains come organic matter in large quantities is 
washed into the crevices and the acidulated waters reach considerable 
depths very promptly. 
The Bearing of Uniformity on Uniformitdrianiain. W. M. Davis, 
Cambridge, Mass. When a theory accounts not only for the facts that 
it was made to explain, but as well for a number of facts that were un- 
known at the time of its suggestion, its correctness isdoul)ly confirmed. 
The early British geologists, who proposed to explain the past history of 
the earth by processes of the same order as those in op'M-ation to-day, 
had the general proV^Iems of denudation and deposition in mind, but 
they knew nothing of several special problems of denudation that are 
encountered in the study of rivers. Even Lyell defended the marine 
origin of the cliffs of the Weald in southeastern England. The doctrine 
of uniformitarianism successfully routed the hypotheses that explained 
valleys as the work of ocean currents during a time of submergence, or 
as the result of fractures in the earth's crust; but the British school, by 
whom this doctrine was so aljly advanced, did not carry it to to the ex- 
treme application of accounting for the migration of river divides and 
the associated adjustment of river courses to rock structures. A fe<v 
British writers have touched this problem, but none of them have pene- 
trated it. European and American geologists have the chief credjt of 
its solution. 
The deepening of young valleys by the ordinary action of streams is a 
comparatively slow process, and the wasting of valley sides under the 
