276 



SCIENCE 



[N. S. Vol. XL. No. 1025 



believe that the climate of the districts fring- 

 ing the ancient ice sheets was of exceptional 

 severity, and that denudation must have pro- 

 ceeded vrith much greater vigor during the 

 later stages of the Ice Age than under the 

 more temperate conditions of the post-glacial 

 period. It would, in fact, be a great mistake 

 to accept denudation as a measure of time, 

 when we are dealing with such variable rela- 

 tions of temperature and precipitation as ap- 

 pear to characterize the Quaternary. 



" In the present state of our knowledge it is 

 impossible to draw a definite line separating 

 the older and newer drifts. Large areas can, 

 however, be distinguished as belonging to one 

 sheet or the other." 



Notwithstanding these statements, a text fig- 

 ure is introduced on the same page (p. Y6) 

 outlining the probable limits of the glaciation 

 represented by the newer drift of the British 

 Isles. Also on pages 78-81 an interglacial 

 shell-bearing clay at Kirmington, in North 

 Lincolnshire, is discussed in detail and shovm 

 to be both overlain and underlain by boulder 

 clay. There is no question that the strati- 

 graphic relations are primary and undis- 

 turbed. The author, however, endeavors to 

 guard the reader against making too much of 

 this section, for he says, page 81 : 



" The extent of this ' interglacial ' retreat 

 need not have been very great and we have very 

 little evidence as to its duration. That it was, 

 however, something more than a mere oscilla- 

 tion of the retreating ice margin seems to be 

 indicated by the marked difference in denuda- 

 tion exhibited by the older and newer drifts." 



The author appears to have been sufficiently 

 impressed by the work of Penck and Briickner 

 in the Alps to accept their interpretation that 

 there was a fourfold repetition of the foreland 

 glaciation. He even goes so far as to present 

 the diagram (Fig. 48) by Penck, representing 

 the supposed relative length of the postglacial 

 and interglacial stages. Concerning " Die 

 Alpen im Eiszeitalter " by Penck and Briick- 

 ner, he states that this marvelous work gives 

 us a glimpse into what may possibly be ef- 

 fected when its exact method and acute reason- 

 ing come to be applied to other districts. 



In the discussion of the glaciation of North 

 America 15 pages are deemed sufficient to 

 cover this most extensive of the fields of 

 Pleistocene glaciation, in which the several 

 drift sheets are more broadly exposed to view 

 than in any other field, and in which the in- 

 cisive methods instituted by Chamberlin have 

 been actively carried on for over 30 years. No 

 mention whatever is made of the oldest drift 

 sheet, the pre-Kansan or Jerseyan, or of the 

 mammalian remains found in the Aftonian. 

 beds which separate the pre-Kansan from the 

 overlying Kansan drift, and which show 

 clearly that conditions favorable for the exist- 

 ance of large herbivorous mammals prevailed. 

 The Kansan, Elinoian and lowan drift sheets 

 are thrown together as " extramorainic," while 

 the Wisconsin drift is classed as " intramo- 

 rainic." The fact that the Ulinoian drift is 

 morainic at its border in southeastern Iowa 

 and western Illinois, and that it embraces sev- 

 eral recessional moraines, seems to have es- 

 caped his attention. The loess he makes use 

 of to mark the separation between the " extra- 

 morainic " and the Wisconsin drift, the former 

 drift being covered by loess, except a part of 

 the lowan, which he thinks should have been 

 covered by it — in order, perhaps, to simplify 

 matters for monoglacialistic interpretation. 



The conclusion is drawn on page 167 that 

 the whole American classification is ready to 

 go to pieces because certain American glacial- 

 ists have expressed doubt concerning the lowan 

 drift. The " agnosticism " which a few Brit- 

 ish glacialists have come to feel on the inter- 

 glacial question is interpreted, without justifi- 

 cation, to have pervaded the entire rank of 

 glacialists in Europe in their attitude toward 

 the northern drifts, the following statement 

 being made on page 167 : 



" It is interesting to note that the apparent 

 ease and definiteness with which the Ameri- 

 cans have read the records of their glacial de- 

 posits is gradually becoming reduced to a state 

 of agnosticism very similar to that of the 

 European glacialists toward their northern 

 drifts." 



The supercritical spirit displayed in refer- 



