112 The American Geologist. February, i904. 
the product of the interaction of several factors, atmospheric, 
geologic, geographic and astronomic, and all these so delicately 
balanced that any slight change may cause great effects. 
We are living in a glacial period. The waning glaciers of 
the Pleistocene are still found in every quarter of the globe. 
But within a generation the northern glaciers have shrunk in 
conspicuous ' degree, although the metorologic data have given 
no certain hint of climatic change. It may be that decrease in 
snow fall is a greater factor in the shrinkage of the Alpine and 
Alaskan glaciers than increase of temperature. And it is prob- 
able that climatic changes which would be competent to produce 
a rapid growth of the existing glaciers might occur and yet be 
so imperceptible as to be undetermined by less than a century 
of accurate observation. 
DIASTROPHIC MOVEMENTS. 
That mountain systems have been formed by lateral or tan- 
gential pressure and consequent crumbling of the strata is a 
fact of observation. The apparent Cause of the mountain- 
making compression is shrinkage of the globe. Under the 
nebular hypothesis a difficulty is here met which has never been 
squarely faced, but like so many other contradictions of facts 
by the old hypothesis has been neglected in the hope that some- 
time, somehow the explanation would be found. The amount of 
tangential compression which the physicists allow to the crust 
of the cooling globe is insufficient to account for theactual short- 
ening which has occurred in the making of the many mountain 
S3'Stems. Mallet estimated that the earth had shrunk from the 
molten state 189 miles in diameter, a circumferential reduction 
of less than 600 miles, and most of this must have taken place 
during solidification and in the stages of high temperature. 
But nearly all the great existing mountain systems have been 
formed since later Paleozoic time, since which time the secular 
contraction must have been very small. Claypole estimated the 
amount of shortening in the Appalachians as 88 miles, and 
Heim estimates the same eiTect in the Alps as 72 miles. 
Under the new hypothesis the earth-shrinkage is due to 
original porosity and gravitational compression, and is in active 
operation today. The amount of such spacial reduction has 
not been estimated, but it must be several times anv possible 
reduction due to cooling. The ocean represents elimination of 
