542 



SCIENCE 



[N. S. Vol. XLI. No. 1058 



On the contrary, the memoir cited is a most 

 vigorous argument in favor of the glacial 

 theory of fiord formation. In it Tarr writes: 

 " Of all the hypotheses proposed, glacial 

 erosion alone appears capable of explaining 

 all the facts. . . . The facts set forth in this 

 chapter prove conclusively that ice has eroded 

 in this inlet to a remarkable degree. . . . 

 Those who oppose vigorous glacial erosion are 

 in the position of those who opposed river 

 erosion long after the majority of workers ac- 

 cepted it — that of ultra-conservatism." ^ 



Gregory cites Mendenhall's discussion of 

 differential warping in the Cook Inlet region 

 of Alaska, and continues : " These two fiords, 

 therefore, according to Mendenhall, occur along 

 a depression due to earth-movements, and the 

 same explanation offers the simplest interpre- 

 tation of many other Alaskan fiords and fiord- 

 straits. They appear to be of tectonic rather 

 than of glacial origin" (324). But Menden- 

 hall's report conveys a very different idea.^ 

 He shows that normal river valleys were oc- 

 cupied by glaciers which " greatly modified " 

 them, and that then these glacially modified 

 valleys were submerged by a depression of the 

 land. Only later, after the fiords had already 

 been in existence for some time, began the 

 differential warping cited by Gregory. As 

 this was an unequal uplift, it tended to de- 

 stroy fiords by raising them above the sea-level, 

 not to make them. It is difficult to under- 

 stand how even an enthusiast for the tectonic 

 theory could find in this faint differential up- 

 lift an argument for the tectonic origin of 

 the deep-cut Alaskan fiords. The same might 

 be said of the author's appeal to the differen- 

 tial uplift of the Labrador Coast, as described 

 by Daly, as an explanation for the rock basins 

 and thresholds of Labrador fiords (283) ; for 

 it is impossible to see how the slight warping 

 of a little more than one foot per mile de- 

 scribed by Daly, could account for the re- 



2E. S. Tarr, "The Yakutat Bay Eegion, 

 Alaska," U. S. G. S., Professional Paper 64, p. 

 118, 1909. 



3W. C. Mendenhall, "A Reconnaissance from 

 Eesurrection Bay to the Tana Eiver, Alaska, in 

 1898," U. S. G. S., 20th Annual Eeport, Pt. VII., 

 332-34, 1900. 



Versed slopes of more than 250 feet per mile 

 in the fiords. 



Spurr is also quoted in support of the tec- 

 tonic origin of Alaskan fiords. Gregory 

 writes : " According to Spurr the lake-basins 

 are preglacial. He says that ' all the lakes of 

 southwestern Alaska, so far as observed by the 

 writer, occupy mountain-valleys which are 

 evidently the ancient river-valleys of the late 

 Miocene'" (319). This quotation from 

 Spurr says nothing at all about the preglacial 

 age of the lake basins. The preglacial age of 

 the valleys alone is indicated; and the context 

 from which this quotation was taken makes it 

 quite clear that the lakes, and consequently 

 their basins, are of more recent date.* 



Gregory's interpretations of his field obser- 

 vations do not always carry conviction. 

 Photographs and sketches of typical glacial 

 troughs with well-developed catenary curves 

 are described as " V-shaped valleys " and 

 " normal denudation curves," apparently be- 

 cause slight bendings of a trough cause the 

 distant profile of one trough wall to intersect 

 the foreground of the opposite wall (Plate V., 

 Figs. 73d, Y3e). It is truly remarkable that 

 such a drawing as Fig. 73d could be cited by 

 any one as a " V-shaped valley " ; but even 

 more remarkable is the author's attempt to 

 show that the well-known contrast between 

 the forms of glaciated and non-glaciated val- 

 leys does not exist (425-32). Although the 

 author has traveled widely, he " can not re- 

 member to have seen any considerable moun- 

 tain-chain or mountain-area in any non- 

 glaciated district which does not show trun- 

 cated spurs, spurless walls and hanging val- 

 leys " (447). The supposed tectonic origin of 

 Cattaro Bay, one of the Dalmatian " fiords," is 

 illustrated by a beautiful photograph of the 

 bay, in which what appear to be triangular 

 " fiat-irons " or hogbacks formed by resistant 

 layers in the folded beds, are described as " tri- 

 angular facets due to faulting" (Plate VT.). 



Many readers will hesitate to accept Greg- 

 ory's arguments because of the significant 



* J. E. Spurr, ' ' A Eeeonnaissance in Southwest- 

 ern Alaska in 1898, " U. S. G. S., 20th Ann. Eept., 

 Pt. VII., p. 258, 1900. 



