MEDITERRAXEAXS COMPARED WITH GEOSYNCLIXES 195' 



oceans that are much more completely hemmed in by continents. It is 

 true, however, that both types of marine areas are greatly depressed deep- 

 water basins situated hetiveen continents. Geosynclines, in the American 

 sense, on the other hand, are long and narrow shallow-water inland seas 

 lying wholly upon a continent (see map, figure 3). 



As the grandeur of European geolog}^ lies mainly in the mountains of 

 the Mediterranean countries, their history and orogenies are well known, 

 and it was but natural for the geologists of Europe to apply the term 

 geosyncline to the area of the Tethyian deposits; all the more so since 

 Dana, the author of the term, used it in several senses. He says :^^ 



"That there were profound geosynclines over the oceanic basins during the- 

 later Tertiary and early Quaternary is put beyond question by the fact of the- 

 great continental elevations of the same time. The Coral Island subsidence,, 

 announced by Darwin in 1839, recognized such geosynclines; and they were 

 long since set forth by Dana as the counterpart of the continental movements." 



It is, therefore, but a natural conclusion for Pirsson to say^° that geo- 

 synclines as well as geanticlines "may occur on the continents, as well as 

 on the ocean floor." 



From these quotations we see that the term geosyncline has been al- 

 tered from the original sense of Hall to the wider one of Dana, and that 

 it is now applied to all marine basins of long-continued sinking and 

 stratal accumulation. This condition of things has become so thoroughly 

 engrafted in the literature of geology that it is probably impossible to 

 change it. We will therefore use the term geos}Ticline in the generic 

 sense, as extended by Dana, and apply it to all the greater long-continued 

 down-flexured parts of the lithosphere. AVith this limitation, rifts and 

 graben are excluded. 



Of such crustal flexures, there are at least four categories. These are 

 as follows : 



2I0X0GE0SYNCLIXES 



The true geosynclines as originally defined by Hall and Dana, which 

 finally give rise to but one synclinorium, are exemplified by the Appa- 

 lachian geosyncline. They are long and comparatively narrow, deeply 

 subsiding, but always shallow-water, smaller, primary geosynclines, situ- 

 ated within a continent along the inner side of borderlands. They should 

 hereafter be known as mono geosynclines, because they are the simplest of 

 geos}T[iclines. 



3» J. D. Dana : Manual of geology, 4th ed., 1895, pp. 936-937. 



« L. Y. Pirsson : Text-book of Geology, Ft. I, Physical geology, 2d ed., 1920, p. 305., 



