Prof. S. W. WUUston—The Fiiujers of Pterodactyls. 59 



been obscured by the idea of an ' Interglacial ' period [Inter glazial- 

 ismus), which has diverted the attention of most observers chiefly to 

 the two moraines, with the supposition that these have originated 

 at widely different times. 



5. If the ' upper moraine ' had represented a separate ice-age, 

 preceded by a long Interglacial epoch with an ameliorated climate, 

 it ought to contain abundant vegetable remains. Plentiful traces 

 of forest-growth should, in this case, have been found embedded 

 in the moraine, for this 'upper' drift, unlike the 'lower moraine,' is- 

 not thick enough to bury and conceal the debris of any land-surface 

 that might have existed outside the ice. 



The stratified deposits of sand and gravel which lie between the- 

 two boulder-clays are most readily explicable as being, from the 

 beginning, of intermorainic origin. In many cases they have 

 probably been formed in ice-dammed water-filled basins over which 

 the thin border of the ice-sheet was buoyed up, thus allowing the 

 subglacial streams to deposit their sand and gravel below the ice 

 which contained the internal 'upper' morainic material. 



To this series of deposits belongs also the Rixdorf Sand. The 

 great extent and thickness of the latter, as well as the manner of 

 its stratification (sand altei'nating with coarse gravel and shingle, 

 frequently showing conspicuous false bedding), clearly indicate that 

 this deposit is glacial; for what streams could deposit such thick 

 beds, including coarse gravel and shingle, on a plain, except under 

 Glacial conditions ! The fauna of the Kixdorf Sand is a mixed 

 fauna ; the fossils are exclusively, or at least principally, found in 

 the coarse gravel, and must be derivative. This opinion regarding 

 the Rixdorf Sand is maintained also by W. Wolff and G. Miiller 

 [ProtoJcoll der Januarsitzung, 1902, der Deutsch. Geol. Gesellscli.). 



Thus, in the opinion of the writer, the evidence tells strongly 

 against the idea of an Interglacial Period. The crux of the matter 

 lies in the correct interpretation of the two moraines. It has been 

 shown that these belong to one and the same period of glaciation ; 

 and it is further held that the so-called ' Interglacial ' deposits 

 themselves, when correctly interpreted, afford confirmatory evidence 

 to the argument against the ' Interglacial ' hypothesis. 



III. — The Fingers of Pterodactyls. 

 By Professor S. "W. Williston, University of Chicago. 



AS is well known, all pterodactyls have three small, unguiculate 

 fingers on the radial side of the patagial finger, evidently used 

 in the support of the body, possibly also in prehension and ambulation. 

 In the older forms these fingers were relatively much better 

 developed than in the later ones, the metacarpals of the former, 

 of considerable strength, all articulating with the carpus, whereas 

 in the more specialized forms of later geological age the proximal 

 ends of these bones had become either greatly attenuated or entirely 

 lost. In Nyctosaurus, for instance, the very small anterior metacarpals 

 were not more than one-eighth of the length of the wing-metacarpal. 



