32 PROCEEDINGS OF THE CHICAGO MEETING 



Certain geologists liave laid a criticism against Suess, claiming that his 

 mechanics of the production of the mountain arcs is at fault, in that the 

 crustal material from which Suess derives the fold-mountains of a given arc 

 are supposed to have moved outward from the relatively small area within 

 the arc, moving from a center toward three sides. This point is discussed in 

 the paper, and it is made clear, in Suess's own words, that this is not his con- 

 ception of the mechanics of the mountain arcs. The mechanics of mountain 

 arcs and lobes, under Suess's interpretation of these forms, is set forth briefly 

 and the dependence of these ideas on Suess's broader views of crustal move- 

 ments on continental scales is discussed. A number of examples of particular 

 mountain forms which strongly support Suess's interpretation are considered 

 in their bearing on the general problem of the origin of the earth's principal 

 features. 



Presented by title in the absence of the author. 



DOCTRINE OF TI-LE ZONE OF FLOW CHALLENGED 

 BY W. H. HOBBS 



(Abstract) 



The idea of a zone of flow within the lithosphere, a doctrine which was de- 

 veloped by Van Hise, requires for the process of rock folding that the strata 

 involved shall support a load which is equal to or greater than their crushing 

 strength. This doctrine seems to have been generally accepted by geologists, 

 though correction of the figures for crushing strength have been made so as to 

 apply to hydrostatic conditions and have carried the depth of the upper limit 

 of the zone of flow to several times that which was estimated by Van Hise. 



When this doctrine is applied to the explanation of an angular unconformity, 

 vertical displacements of strata become necessary which have magnitudes 

 great enough to carry the interpretation perilously close to an absurdity. 

 Reasons are given for believing that the element of time has not been given 

 sufficient weight in reaching the conclusions, and recent work in the Pacific is 

 cited to show that folds are today actually taking place at and above the 

 present level of the sea. 



Presented without manuscript. 



CRUSTAL DEFORMATION IN THE PACIFIC AND ATLANTIC REGIONS 

 BY W. H. HOBBS 



■ (Abstract) 



The recent study of earthquakes from remote stations has proven conclu- 

 sively that the larger movements of the earth's crust which are now going on 

 have taken place near, though largely inside, the borders of the Pacific Ocean, 

 though there is a strong subordinate zone which follows the twin plane of the 

 intercontinental seas, thus conforming quite closely in direction with the floors 

 of deposition for the Mesozoic era. Outside these zones the lithosphere sur- 

 face may be described by contrast as in repose. The contrasted conditions for 

 the Atlantic and Pacific regions are therefore striking. 



