632 DYNAMICAL GEOLOGY. 



1. Drift-sand Accumulations. — The amount of sand transportation 

 is greatest, other things equal, where there is no covering of vegeta- 

 tion to keep down the sands ; and the deposits made are most exten- 

 sive in the direction of the prevailing currents. The interior of con- 

 tinents are by nature mostly free from drift sands, owing to the wide 

 spread prairies and forests, excepting certain arid or desert regions, 

 and small local areas. Windward sea-coasts are the localities where 

 drifting goes forward most rapidly. The seashore is commonly a 

 narrow strip of incoherent sands, and this narrow strip is the margin 

 of a broad region of loose sands extending out in the shallow waters. 

 The winds, blowing across the beach and the sand-laden breakers, 

 take up the sand and carry it beyond the beach, where it forms, 

 nearly parallel with the coast, what are called sand-drift ridges or 

 hills. They are made especially where the sands fire almost purely 

 siliceous, and hence are inadhesive, and little fit for any kind of vege- 

 tation. They have often a height of thirty feet, and sometimes of a 

 hundred, as on the east side of Lake Michigan. They take their 

 greatest height on projecting coasts that receive the winds from differ- 

 ent directions. 



On the south side of Long Island such ridges extend along for a hundred miles, and 

 they vary in height from 5 to 30 feet. The coast of New Jersey, down to the Chesa- 

 peake, and others farther south, are similarly fronted by sand-hills. In Norfolk, Eng- 

 land, between Hunstanton and Weybonrne, they are 50 to 60 feet high. On the north 

 side of Oahu, one of the Hawaiian Islands, they are 30 feet high; and on the coral 

 islands of the Pacific the windward points sometimes receive thus a height of 20 or 30 

 feet, while the leeward side may have not even a beach. They form along the shores 

 also of large lakes. On the east side of Lake Michigan, according to A. Winchell, the 

 sand-hills reach a height of 100 to 200 feet; they are 215 feet high at Grand Haven, and 

 30 to 93 near New Buffalo. Lyell speaks of drift-hills on the north coast of Cornwall, 

 several hundred feet above the level of the sea. 



These accumulations have the peculiar kind of quaquaversal strati- 

 fication described and figured on page 82 (Fig. 61 d). Curving planes 

 in the lamination show former shapes of the hill ; and abrupt changes 

 of direction, indicate that the growing hill was cut partly down or 

 through by storms, and was again and again completed after the disas- 

 ters. The forms of snow-drifts are a good study with reference to the 

 natural forms of sand-drifts. 



The old sand-hills on northern Oahu, made of coral sand, have become consolidated; 

 and sections of them exhibit well, on some of their sides, this style of lamination. The 

 Pictured Rocks of Lake Superior at some places have the same character, and evince 

 that the beds are in part drift-sand accumulations. 



Such seashore driftings are a means of recovering lands from the 

 sea. The sea first makes the sand-flats or beaches, and then the winds 

 do the rest. Lyell observes that, at Yarmouth, England, thousands of 

 acres of land now under cultivation have been thus gained from a for- 

 mer estuary. 



