(3S7) 



The sequence of events which has resulted in the formation 

 of this area of land was evidently identical with that which 

 is adding to it to-dav. It is doubtful in fact if there has been 

 any interruption since the time when the first shoal or sand 

 bar began to form north of the Highlands of Truro, except 

 such as has been caused by the influence of man. This 

 sequence evidently began with the erosion of the older part of 

 the cape, or, more correctly, of the land which now forms the 

 cape. The prevailing northward trend of the tides and cur- 

 rents transported the eroded material to and beyond the 

 northern extremity of the land, where it was dropped in the 

 slack water of the currents as they swept around into Cape 

 Cod Bay. A submarine shoal or bank was thus formed, which 

 subsequently developed into a sand spit, extending out from 

 the original land. This continued to extend northward and 

 westward, following the curve of the currents, while its older 

 part was being built up permanently, above the level of the 

 highest tides, by wave and wind action. It also began to 

 extend laterally by reason of the sand drifting in the direction 

 of the prevailing winds. In the slack water on the inner 

 side of the sand spit the tide continued to ebb and flow for a 

 greater or less length of time, but finally it became silted up 

 and converted, first into tidal flats and subsequently into a 

 salt marsh, which was eventually obliterated, either wholly 

 or in part, by drifting sand and covered to a greater or less 

 extent by dunes. 



On the accompanying map (Plate 40) the principal surface 

 and submarine features are indicated, in order to illustrate 

 how these successive steps in land formation have taken 

 place. The twenty-foot contours above ocean level are 

 shown and most of the higher points within these contours 

 are noted by figures, while many of the depressed areas are 

 represented by the recognized topographic signs for swamps 

 or ponds as the case may be, where such exist. The sur- 

 rounding submarine area, where shoals or bars are now form- 

 ing, or have formed in recent years, is also included. Changes, 

 both on land and under water, are constantly taking place 



