902 PRINCIPLES OF STRATIGRAPHY 



and he explains this by the supposition that the geosyncHne was 

 located between two continental masses and not, as held by Ameri- 

 can students, on the borders of the continent. He holds that the 

 geosynclines are zones of weakness and mobility between two rela- 

 tively stable masses. 



The Plimalayas are chosen by Haug as an illustration of a great 

 geosyncline (in pre-mountain time) formed, not on the border of 

 a sea, but between two continental masses, the stable Indian land 

 mass on the south and a similar land mass on the north. In spite 

 of this location, he holds that Palaeozoic and IMesozoic sediments in 

 this geosyncline are none of them of a littoral (neritic) character. 

 The chains of central Europe are in like manner regarded by Haug 

 as occupying the sites of former geosynclines. If the expanded 

 ]\Iediterranean basin of Mesozoic time is to be considered in the 

 light of a geosyncline, the bathyal nature of some of the sediments 

 therein, or at any rate their thalassogenic character, may be readily 

 conceded. It may be questioned, however, if the use of the term 

 geosyncline for an intracontinental sea' with abyssal regions (i. e.. 

 a mediterranean ) is permissible. Certainly such a condition did 

 not prevail in the Pakeozoic of the Appalachian region. Here an 

 accumulation of 40,000 feet of sediment was accompanied by a 

 downward bowing of the sea-floor bordering the old Appalachian 

 continent. P.ut this was probably never of great depth, nor was 

 there, as a rule, a land mass to the west of the region of sedimenta- 

 tion. Indeed, as has already been pointed out. and, as has elsewhere 

 been discussed by the author in great detail, the prevailing sedi- 

 ments were of shallow water and terrestrial type. As stated in 

 Chapter XX, it seems best to restrict the name geosyncline to such 

 regions of deposition, and use the name fore-deep for regions 

 known to have descended to bathyal or abyssal depths. That these 

 fore-deeps are due to tectonic movements is freely conceded, but 

 the geosyncline of the Appalachian type is most probably due to 

 isostatic readjustments incident ui)on the loacHng of the earth's 

 surface along the line of subsidence. This does not imply, how- 

 ever, that the subsequent folding of these strata is due to any 

 other cause than that of yielding under compressive strain. Such 

 an origin alone seems to be possible, in view of the many features 

 which can be explained only as originating under compressive 

 stresses. 



Geosynclines the Sites of Orogenic Disturbances. As long 

 ago pointed out by Hall and Dana, and as emphasized by Haug, 

 the geosynclines are the sites of subsequent foldings of the strata, 

 or, conversely, the regions of folded mountains are the sites of 



