364 



SCIENCE 



[N. S. Vol. XLVII. No. 1215 



contribution towards the cost of equipment 

 of the new department of geology. 



Haeold Ernest Burtt has been appointed 

 instructor in psycliology at Harvard Uni- 

 versity. 



The first incumbent of the newly founded 

 chair of phthisiology at the University of 

 Edinburgh is Sir Eobert W. Philip, professor 

 of clinical medicine, said to be the founder of 

 the first antituberculosis dispensary. 



DISCUSSION AND CORRESPONDENCE 



EVIDENCE FROM[ ALASKA OF THE UNITY OF 

 THE PLEISTOCENE GLACIAL PERIOD 



To THE Editor of Science : In an article en- 

 titled " Frozen Muck in the Klondike Dis- 

 trict, Yukon Territory, Canada," by J. B. 

 Tyrrell, of the Canadian Survey, published in 

 the Transactions of the Boyal Society of 

 Canada, Series III., 1917, Volume XI., pages 

 39-46, there is a remarkable collection of facts 

 seeming to prove the unity and continuity of 

 the Pleistocene Glacial Period. It is true that 

 there was no extension of moving glacial ice 

 over the Klondike region, but there is abun- 

 dant evidence of a change of climatic condi- 

 tions corresponding to that of the generally 

 glaciated region of the continent. During the 

 warmer climate of the Tertiary period the 

 streams had built up extensive gravel deposits 

 over the bottoms of many of the valleys. Eor 

 a long period " the climate had been temperate, 

 or at all events, not arctic, and large numbers 

 of animals, such as bison, mammoth, elk, 

 moose, horse, etc., had roamed over the 

 country. 



Suddenly, a new set of climatic conditions be- 

 gan to prevail. The Glacial Period tiegan, and, 

 while the vast sheets of ice which covered so large 

 a portion of Canada during that Period never ex- 

 tended over the Klondike district, the cold un- 

 doubtedly became very intense, and as a conse- 

 quence the ground became permanently frozen. 

 With the freezing of the soil and of the underly- 

 ing rock the processes of oxidation and disiate- 

 gration of this rock were no longer possible, and 

 the small tributary brooks which flowed over the 

 frozen land into the main streams were no longer 

 able to collect and wash down sand and gravel 

 from it. The supply of sand and gravel having 



been thus cut off, it could no longer be distrib- 

 uted by the main streams over the alluvial flats as 

 it had been distributed before, but nevertheless the 

 sand and gravel flats themselves were not worn 

 away by the streams as they would have been under 

 normal conditions, for they were cemented into 

 very resistant masses by a matrix of ice. 



The sand and gravel so deposited and preserved 

 on the alluvial flats is now overlain by a deposit of 

 vegetable material locally known as "muck," 

 which may have a thickness of ten, twenty, thirty, 

 or even as much as one hundred feet. The plane 

 of separation between the gravel and "muck" 

 is usually sharp and well defined, though occa- 

 sionally little layers of "muck" may be found 

 included in the upper beds of the gravel. The gen- 

 eral impression that a person gets from a study of 

 the deposits, however, is that of a sudden change 

 from gravel to "muck" (pp. 40, 41). 



The significant thing is that this layer of 

 muck whose formation started in a period of 

 great cold in early glacial times, has gone on 

 continuously and uniaterruptedly accumula- 

 ting down to the present time. The bones of 

 the extinct animals above enumerated " are 

 found in large numbers in the underlying 

 gravels and in the bottom of the muck ; but the 

 climate would seem to have soon become too 

 inhospitable for them, and their remains are 

 very scarce in the higher portions of the muck 

 and finally disappear from it altogether" (p. 

 45). Dr. Tyrrell believes " that a critical study 

 of the plant remains from the various layers 

 of the muck might furnish much interesting 

 information as to the character and climate of 

 that portion of the world, in which there has 

 been a continuous formation of vegetable beds 

 from the beginning of the Glacial Period 

 down to the present " (p. 46). The bearing of 

 all this upon the unity of the Pleistocene Gla- 

 cial Period is too evident to need statement. 

 G. Frederick Wright 



Oberlin, 



drawings on lantern slides 

 It often occurs that one wishes to inter- 

 pose diagrams or line drawings in a class- 

 room lecture which is being illustrated by 

 lantern slides, and one has to either forego 

 the point entirely, or turn on the lights and 

 use a chart, or put the necessary diagram or 



