556 PROCEEDINGS OF THE WASHINCxTON MEETING 



government charts; there are a number of early maps of this coast which are in 

 the main little more than sketches, and yet when these sketches are studied with 

 reference to other facts, interesting inferences may be drawn ; there are many 

 traditions of the island and its changing shoreline which are worthy of considera- 

 tion in a comprehensive study of the development of the island ; there are facts in 

 the early history of the island, such as the settlement on Capaum harbor, now a 

 pond, which throw light on the development, and, more than all, there are small 

 changes from year to year in various parts of the island, which if carefully and 

 systematically recorded will throw much light on the past history of the island in 

 the present cycle of its development, and which may also increase our knowledge 

 of the general development of shorelines. 



The writer proposes to undertake the study of this island along all of the lines 

 mentioned above, and to report to the Geological Society of America the results of 

 his investigations in a series of papers. The plan of work will be to take up in 

 detail the various points where changes have been made in the })ast or are made 

 in future years by cutting away or building up, and to publish detailed plane-table 

 maps to show present conditions. These maps may be used for comparison in 

 future years. 



The following areas will be taken up in succeeding papers : Great point, Coskata, 

 Haulover break, Squam head, Sankaty head, 'Sconset, Tom Nevers, Nantucket 

 shoals, South shore, Surfside, Maddaket, Smith point, Tuckernuck island, Tucker- 

 nuck shoals, Muskeget island, Muskeget shoals, Eel point, Capaum, Brant point, 

 Nantucket harbor, Coatue, Abrams point. Polpis harbor. 



After the facts for these areas have been studied, the history of the development 

 of this region in the present cycle will be worked out. 



TIMBERLINES 

 BY ISRAEL C. RUSSELL 



\_Ahstract] 



" Timberline," as commonly defined, is the up[)er limit of arboreal vegetation 

 on mountains. Its position is determined mainly by the occurrence of a mean 

 annual temperature of about 32 degrees Fahrenheit, but locally its elevation is 

 regulated by soil conditions,' and by diflferences between various localities in snow- 

 fall, severity of winter storms, exposure to the sun, etcetera. It may with pro- 

 priety be termed the "cold timber-line." Above it, on high mountains, there is 

 commonly a region occupied by alpine flowers, and still higher a region of perpetual 

 snow. When traced from warm to colder regions, or, in general, from equatorial 

 toward polar regions, it becomes lower and lower. In North America it descends 

 nearly to sealevel in Alaska and northern Canada, where it defines the northern 

 limit of the subarctic forest and becomes the " continental timber-line," to the 

 north of which lie the barren grounds and tundras, which correspond to the zone 

 of alpine flowers on lofty mountains in temperate latitudes. 



On some of the mountain ranges of the arid portion of the United States there 

 is a lower limitof tree growth, the position of which is determined in the main by 

 insufficient moisture, and locally by soil conditions, including the presence of alkali, 

 hot winds, forest fires, exposure to the sun, etcetera. This may be termed the 

 "dry timber-line." Below it are treeless, grass-covered plains and valleys. On 



