THE GEOLOGICAL EVIDENCES. 51 



the hypothesis of rotational reduction is concentrated toward the poles, 

 and hence, if tension is to be avoided in high latitudes, a very much larger 

 radial contraction than the amount named must be postulated. 



It must also be considered whether cooHng, or any other similar con- 

 tractional agency that can be postulated consistently with the early states 

 of the earth assumed by this hypothesis, would be competent to offset the 

 tensional effects imposed by the change of rotation in the polar regions. 

 ^ ^ If, to escape the difficulties arising from exceptional tension in high 

 latitudes, it be assumed that the whole shell of the lower latitudes crowded 

 toward the poles, this would involve meridional crowding and the forma- 

 tion of a system of folded ranges pointing to the poles, while east-and-west 

 ranges should be absent proportionately, and thus the effects should be 

 expressed in a distinctive manner. So it seems safe to conclude that, in 

 one way or another, the high-latitude tension should have expressed itself in 

 a characteristic way and, on account of its magnitude, its expression should 

 be declared. 



In comparing the facts with the theoretical requirements it must again 

 be noted that the earlier formations should show the most evidence of 

 tension, the Archean most of all. As a matter of fact, the Archean of high 

 latitudes, as of low latitudes, shows abounding evidences of compression. 

 It was my privilege in 1894, as geologist to the Peary Auxiliary Expe- 

 dition, to see something of the ancient crystalHne rocks of Greenland at 

 latitudes as high as 77°. They bore the same evidences of crumpling, 

 contortion, fohation, and thrust-stress generally as are commonly shown 

 by the Archean rocks in lower latitudes. All descriptions of high-latitude 

 formations of this age are identical in dynamic characters with those of 

 lower latitudes, so far as my knowledge extends. The Archean terranes 

 of Scandinavia and Finland lie far within the area of hypothetical tension, 

 as do also those of Scotland and Canada, and even those of central Europe 

 and the northern United States. The Archean and Proterozoic rocks of 

 these regions bear evidences of tangential thrust of a most declared type, and 

 no distinction between the most ancient rocks of the high-latitude and the 

 low-latitude regions, in the matter of compressional characters, has, I believe, 

 ever been detected. The Hterature of the subject does not show any special 

 distribution of veins, dikes, normal faulting, and other evidences of tensional 

 stresses correspondent to latitude. Apparently these features are essentially 

 as prevalent in the equatorial belt as in the polar circles. 



If the equatorial belt has been subjected from the beginning to constant 

 increments of tangential stress and of gravity (column 4 of Slichter's table, 

 page 67) while the polar regions have been concurrently subjected to incre- 

 ments of tension and decrements of gravity (column 5), it would seem that 

 volcanic action would always have found adverse conditions in the former 

 region and favorable ones in the latter, certainly so if pressure is adverse 

 to liquefaction and if tensional faulting facilitates eruption. It does not 

 appear, however, that volcanoes are in any appreciable degree infrequent 

 in the tropical zone or that they are specially frequent in high latitudes. 

 The prevaihng impression is that they are somewhat more abundant in 

 the tropics than in high latitudes, but there is little, if any, warrant for any 

 latitudinal discrimination. 

 4 



