The salt marsh at Barnstable, Massachusetts, occupies an embayment into which it has spread during the past 4,000 years. It exhibits all stages of development from the seeding of bare sand flats through the development of intertidal marsh to the formation of mature high marsh underlain by peat deposits more than 20 ft deep. Observations and measurements of the stages of its formation are presented. The geomorphology of the marsh is considered in relation to the factors which have influenced its development, i.e., the ability of halophytes to grow at limited tide levels, the tidal regime, the processes of sedimentation, and the contemporary rise in sea level. The rates at which the early stage of development takes place have been determined by observations during a period of 12 years and the time sequence of later stages by radiocarbon analyses.

The development of a typical New England salt marsh, and the growth of the sand spit which shelters it, during the past 4000 years has been reconstructed from soundings and borings of the peat. The results have been interpreted with the aid of observations on the structure of the marsh and estimates of the rate of its vertical accretion based on carbon-14 determinations.

Exploratory data from more than 1000 analyses of the distribution of deuterium in waters of the North American continent and the surface oceans contiguous to the continent are presented. The elementary theory of the processes that appear to explain the changes in the deuterium content of natural waters is developed. Quantitative expressions of the deuterium fractionation that can be expected to occur are presented for all phases of the hydrologic cycle from the evaporation of water from the oceans, its precipitation as rain and snow, and its travel back to the sea. Processes such as the freezing of water under equilibrium and nonequilibrium conditions, the evaporation of water from closed lakes and from lakes with an outlet, the formation of fog, frost, and dew are also discussed. The regional characteristics of the surface waters of North America are described and interpreted as reflecting the history of the water in the course of the hydrologic cycle.

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What is reported in the following pages is an example of work achieved in a relatively short time by the co-operation of a sufficient number of institutions and individuals. The venue of this research was in the Andes, and the work was carried out in the winter 1921-1922, yet its organisation only commenced definitely in the early summer of 1921, when a group of British and American physiologists secured the support of the various universities or other institutions to which they were attached. This support was given in the most ungrudging way. It included the liberation from immediate duty of the members of the party, often at considerable inconvenience to those who remained at home, the loan of apparatus, the contribution of substantial funds, and a great body of goodwill, which was perpetually translating itself into increased efficiency of the work actually accomplished. The following collaborated in one or more of the ways indicated above:— The Department of Physical Chemistry of Harvard University. The Proctor Fund of Harvard University. The Elizabeth Thompson Fund. The Rockefeller Institute of Medical Research, New York City. Columbia University.—From a fund, to which contributions were made by Dr. Walter B. James, Mr. Cleveland H. Dodge, and a contributor who wishes to withhold his name, but to whom thanks are none the less due. The Royal Society of London. The Research Grant to the Physiological Department of the University of Toronto. The Moray Fund, Edinburgh. The Carnegie Fund, Edinburgh. Sir Robert Hadfield, Bart., F. R. S. Sir Peter Mackie, Bart.

Radioactive carbon determinations of the age of peat indicate that at Bermuda, southern Florida, North Carolina, and Louisiana the relative sea level has risen at approximately the same rate, 2.5 x 10(-3) foot per year (0.76 x 10(-3) meter per year), during the past 4000 years. It is proposed tentatively that this is the rate of eustatic change in sea level. The rise in sea level along the northeastern coast of the United States has been at a rate much greater than this, indicating local subsidence of the land. Between Cape Cod and northern Virginia, coastal subsidence of 13 feet appears to have occurred between 4000 and 2000 years ago and has continued at a rate of about 1 x 10(-3) foot per year since then. On the northeastern coast of Massachusetts, subsidence of 6 feet occurred between 4000 and 3000 years ago; since then sea level has risen at about the eustatic rate. Between 12,000 and 4000 years ago, sea level rose at an average of about 11 x 10(-3) foot per year. The part played by local subsidence or temporary departures from the average rate during this period is uncertain.