June 21, 1918] 



SCIENCE 



615 



and tropical East Africa have reciprocating 

 currents, while the south coast of Australia re- 

 ceives drift from South Africa and southern 

 South America. Similarly southeastern Aus- 

 tralian drift would tend to reach the north 

 end of New Zealand. If the data were only 

 sufficient for the construction of accurate pal- 

 eogeographical maps for those times of land 

 extension during the Tertiary and Quaternary 

 and if the ocean currents could then be plotted 

 upon these, doubtless much light would be 

 shed on many anomalies of distribution. 



"Work like that of Guppy, interesting and 

 important as it undoubtedly is, can hardly be 

 said to furnish more than analogies and a basis 

 for theory, since tlie distribution of most of 

 the orders of plants was a much more ancient 

 process, and imless we are prepared to sub- 

 scribe to similar continental outlines, climates 

 and ocean currents during the Tertiary, all 

 three assumptions which are negatived by what 

 we already know of geological history, we have 

 many other factors than are furnished by ex- 

 isting conditions which must be taken into ac- 

 count. 



The chapters headed Differentiation and 

 Distribution are eminently sound in principle 

 and should give plant geographers much food 

 for thought. It is a great pity that in this 

 connection the author seems to be unfamiliar 

 with considerable recent American literature 

 on this subject. 



A special chapter is devoted to the distribu- 

 tion of Sphagnum and Carex, and the Azores 

 occupy the three concluding chapters, while an 

 appendix contains over fifty additional pages of 

 valuable matter. 



The book is well written and well printed 

 and is a mine of information which is illumi- 

 nated throughout with ideas, and it should 

 find a place in every well-equipped library. 

 Edward W. Berry 



Johns Hopkins Univeesitt, 

 Baltimobb 



SPECIAL ARTICLES 



POST-GLACIAL CONTINENTAL UPLIFT 



The rise and fall of great areas of the earth's 

 surface (diastrophism) is one of the most cer- 



tain facts of human observation. Isostacy, the 

 general equilibrium or balancing of pressures 

 within the earth's " crust," is recognized as a 

 fundamental principle of geophysics. The 

 crust of the earth is sensitive to \mbalanced 

 pressures, the loading and unloading of differ- 

 ent areas. It is, therefore, reasonable to sup- 

 pose that the weighting of large areas of 

 northern lands in Pleistocene time by the ac- 

 cumulntion of vast continental glaciers, one or 

 two miles in depth, would produce subsidence; 

 and that the return of the ice caps to the sea 

 would cause uprising of the depressed areas. 

 Whatever may be the opinion of the stu- 

 dent of geophysics regarding the effect of the 

 Pleistocene ice caps on diastrophie land move- 

 ment, yet the fact is certain that the area 

 covered by the latest North American ice sheet, 

 the Labradorian glacier, stood much beneath 

 its present position, relative to sea level, when 

 the ice sheet melted off; and that a recent 

 slow uplift has brought the land to its present 

 attitude. The proof of this Post-Glaeial up- 

 lift is the occurrence of many high-level 

 beaches and sandplains facing the open sea, 

 and extending far up the valleys in Canada, 

 New England and New York, with the oc- 

 currence of abundant marine fossils himdreds 

 of feet above the ocean. These facts have been 

 recognized for nearly a century, and a great 

 number of observations are on record in 

 Canadian and American geological literature. 

 Yet up to the present time the full vertical 

 amount of submergence, or the subsequent up- 

 lift, and the extent or limits of the affected 

 area have not been determined beyond dispute. 

 The total amount of the down-and-up move- 

 ment has nearly always been underestimated, 

 for the reason that the conspicuous or more 

 evident marine features are of inferior and 

 later levels, while the initial and summit shore 

 features are commonly weak and unobtrusive, 

 or they lie so far inland and are so detached 

 as to be unrecognized, or their origin and re- 

 lationship misinterpreted; usually being re- 

 ferred to glacial agency. Yet the summit or 

 initial level at any locality is the one critical 

 and essential element in the diastrophie prob- 

 lem. 



