merged off the southeastern coast of New England as the result of the postglacial worldwide rise in sea level. The exposed broad coastal plain of low relief provided abundant shallow sedimentary basins in which the gradual Detailed quantitation and integration of chronological and palynological data have not been available for assigning precise values to the latitudinal retreat of the boreal forest during the period of climatic amelioration that began about 11,000 years ago. Evidence needed for such a quantitative approach may be present in the fresh- transition of forest types may have been recorded. Many of the offshore swamps and bogs should have been relatively free of the local edaphic and water autochthonous peats that are sub- 0 { TF 2 t 3 q 4 5 I I : 7 T 8 9 ' 0 q $f fF I *10/- 12 $3 T I 44 45 T SQ he 46 [ i 1B 7 Te 0 ™ w “10r- og - ep wee BS REDFIELD AND uy “207 BARN}e MOH CEN : He-1 OP2 3 M27 KH } xo-40 Re AL oy 4 mB3 rH M26 4 FON FOEreHe-+4RL as ett 2 ~_ bd Q -50;— 4 a$210 butts rOSIN A Om D 47 D26 044 OS 186 “60K t 4 “ -Oe-+RL1I rO4G 2198 70 - HH ROG BARN = = -30/- 1 ! ! i { oo it wl 060 | : An interesting problem of plant physiology is raised by the finding that plants high on the salt-marsh have ratics of stable carbon isotopes similar to L t 1 ree L short length of time that they are submerged. The measurements that were made indicate that 6C™ is a useful means of distinguishing between an- rei B0S RUBIN (1962) paleoclimatology. those of marine plants, in spite of the THOUSANDS OF YEARS AGO 6 physiographic variables that complicate many upland sites of organic deposition, such as the pollen rain from the windward montane forests of the Appalachian Highlands. Accordingly, further work on the offshore peat deposits may be highly rewarding for studies of I Fig. 6. Depths of radiocarbon-dated samples of peat (closed circles) and shells (open circles) whose positions are given by Table 1 and in Figs. 1 and 2. Dates for V and AZ are based only upon their pollen contents. The curved line shows the position of sea level 4000 to 11,000 years ago according to the ages and present depths of oyster shells and of the salt-marsh peat within sample RL1. At the left, the wide straight lines indicate the position of sea level during the past 3800 years according to radiocarbon dates of Barnstable galt marsh (/5). cient salt-marsh and freshwater peats. K. O. EMERY Woods Hole Oceanographic Institution, Woods Hole, Massachusetts R, L. WIGLEY U.S. Bureau of Commercial Fisheries, Biological Laboratory, Woods Hole ALEXANDRA 8S. BARTLETT Department of Biology and Botanical Museum, Harvard University, Cambridge, Massachusetts MEYER RUBIN Radiocarbon Laboratory, U.S. Geological Survey, Washington, D.C. E. S. BARGHOORN Department of Biology and Botanical Museum, Harvard University References and Notes ff “ft 0 e A GLACIERS - aay ge =a XA ud “25° Yo 2°50 x 7 ui?° a “100 -qa5k eta =X J tT t- | CNS= ee Se TeEF oeSe ee ———— Segggygeeaae Fig. 7. Schematic diagram of the relation of freshwater ponds to other environments of New England. Areas marked PONDS are characterized by freshwater peats, LAGOONSbysalt-marsh peats and oyster shells; OCEAN by marine sands and silts, _ and GLACIERS bytill and outwash. 1306 wh 20 P oman Arsbok 51, No. 557, 1 (1957). . H. F. Nelson and E. E. Bray, Program Geol. Soc. Amer, (annual meeting, San Francisco, 1966), p. 150. 6. E. McFarlan, Jr., Bull. Geol. Soc. Amer. 72, 129 (1961). 7. D. M. Churchill, J. Roy. Soe. W. Australia 42, 53 (1959). 8 . T. van der Hammen, Leidse Geol. Mededel. z9, 125 (1963). 9 . G. H. Keller and A. F. Richards, J. Sed. Petrol. 37, 202 (1967). 10. H. Niino, Tokyo Univ. Fisheries, personal communication (1966). V1, J. R. L. Allen, Marine Geol. 1, 289 (1964). 12. K, O. Emery, R. L. Wigley, M. Rubin, Limnol. Oceanogr. 10, R97 (1965). 13. J. M. Zeigler, S. D. Tuttle, H. J. Tasha, G, S. Giese, Bull. Geol. Soc. Amer. 75, 705 (1964), 14. W. M. Sackett, Marine Geol. 2, 173 (1964). 15. A. C. Redfield and M. Rubin, Proc. Nat. Acad. Sci. U.S. 48, 1728 (1962). 16. A. C. Redfield, Science 157, 687 (1967); W. S. Newman and G, A, Rusnak, ibid. 148, 1464 (1965). 17. F. P. Shepard, Essays in Marine Geology (Hancock Foundation, Univ. of Southern California, Los Angeles, 1963), p. 1; K. O. Emery and L. E. Garrison, Science 157, 684 (1967). 18. C. A, Kaye, U.S. Geol. Surv. Prof. Paper SO0I-C (1964), p. 134. 9. J. P. Schafer and J. H. Hartshorn, in The Quaternary of the United States, H. E. Wright and D. G. Frey, Eds. (Princeton Univ. Press, Princeton, N.J.. 1965), p. 113. ta +25 (======rs = sie 1. J. W. Stather, Quart. J. Geol. Sec. London 68, 324 (1912). H. J, Veenstra, Marine Geol. 3, 245 (1965). K. Andrée, Geolegie des Meeresbodens (Gebriider Borntraeger, Leipzig, 1920). . G, Lundqvist, Sveriges Geol, Undersékn, —_ 0 THOUSANDS OF YEARS AGO SCIENCE, VOL. 158