618 



SCIENCE. 



[N. S. Vol. XIV. No. 355. 



worn down in preglacial time to the great depth 

 of the main valley. Moreover, as a rule, the 

 fiord walls are not strongly ravined ; they are 

 generally rather smooth, as if they had been 

 severely scoured. May it nob therefore be sup- 

 posed that the ravi.nes are of late interglacial 

 origin in rock structures that favor relatively 

 rapid wearing ; and that they have been eroded 

 with respect to a valley floor which earlier 

 glacial erosion had already deepened ; while a 

 minimum measure of the total glacial erosion is 

 best given by the altitude of the large hanging 

 valleys above the fiord bottoms, huge as the 

 minimum may be ? 



THE OBIGIN OP MOELS. 



' The Origin of Moels, and their Subsequent 

 Dissection ' {Oeogr. Journ., XVII., 1901, 63-69) 

 is a discussion by Marr of the rounded mountains 

 common in several parts of Great Britain, show- 

 ing convex, dome-like tops and concave basal 

 slopes, all covered with rock waste and vegeta- 

 tion, and nob dissected by streams. Etymolog- 

 ically they are the Welsh equivalents of the 

 'balds' of our North Carolina mountains. Their 

 form is ascribed to weathering under vegetation. 

 The irregular forms into which a tableland is 

 carved by streams would in time be subdued to 

 moels, if weathering under a climate which 

 favored the growth of a mantle of vegetation by 

 which streams are excluded. In an arid or 

 frigid climate, sharp peaks or ridges with even- 

 sloping sides would, it is said, be developed, 

 while running water would carve the well- 

 known concave valley lines with steepening 

 slope to their sources. The author goes on to 

 show that if streams should gain a hold on a 

 moel, either by climatic change destroying the 

 plant mantle or by head ward growth from the 

 basal slopes, radial valleys would be carved by 

 retrogressive erosion. Such valleys would in 

 time reduce the intervening spurs into sharp 

 ridges ; notches would be worn in the narrow- 

 ing ridges near the summit, where they are 

 soonest consumed by the widening valley heads ; 

 and the peak of each ridge, just outside of the 

 notch, would then be a 'tahoma,' as Eussell 

 has called such forms on Mt. Eainier (18th Ann. 

 Eep. U. S. G. S., pt. II., 349). When one side 

 of a mountain is exposed to rainy winds, while 



the other side is relatively dry, the convex 

 moel slope may be paired with the concave 

 stream slope, as in certain parts of the English 

 lake district. 



Soil-creeping might have been given more 

 explicit consideration than it here receives ; for 

 both the convex upper summit and the concave 

 basal slopes of a valleyless moel may be largely 

 produced by the slow creeping of the waste 

 cover, as well as or better than ' partly by the 

 action of the wind, and partly by inconstant 

 runnels of water.' It seems unadvisable to 

 treat moels as exhibiting ' the ultimate out- 

 lines of mountains which have been shaped by 

 denudation ' ; for the ultimate outlines are 

 level to the eye, and even the penultimate out- 

 lines have but a faint relief as the moels fade 

 away. It is questionable whether the attain- 

 ment of a convex summit outline is impossible 

 in arid and frigid deserts ; more pl-obably it is 

 merely delayed till the reduction of the moun- 

 tain to a moderate relief in a late stage of the 

 cycle weakens the forces of waste transporta- 

 tion to essential equality with forces of waste 

 supply ; a graded waste cover may then be 

 formed all over the surface, whose outline will 

 exhibit no sharp forms, but only gentle undula- 

 tions. These undulations may be too gentle to 

 be classed with the strong moels of AVales, but 

 they deserve consideration in the general study 

 of land forms. 



W. M. Davis. 



THE PRYLOGENY OF THE TOOTHED 

 WHALES. 

 A RECENT issue of the Memoirs of the Boyal 

 Museum of Natural History of Belgium is de- 

 voted to a paper by Dr. O. Abel on the 

 ' Longirostrine Dolphins of Bolderien,' in which 

 the author describes and figures in detail the 

 skulls of two remarkable extinct dolphins, Cyr- 

 todelphis sulcalus and Eurhinodelphis cocheteuxi. 

 The memoir is, however, a great deal more 

 than the description of these crania, valuable 

 though this be, for nearly one-half of it is 

 devoted to observations on the phylogeny of 

 the Odontoceti. We have a discussion of the 

 evidence furnished by the dentition in general, 

 and that of the pre-maxillaries in particular, 

 the dermal armor and the general characters of 



