162 DYNAMICAL GEOLOGY. 



drift-hills of projecting capes are seldom over 30 feet high; while at the 

 Bermudas and Bahamas, within the belt of Atlantic cyclones whose winds 

 have often a velocity of 60 to 90 miles an hour, the sands cover great sur- 

 faces, are sometimes quite coarse, and make ridges 100 to 230 feet in height. 

 The highest drift ridges are on the side which receives the winds of the first 

 half of the cyclone. 



On the south side of Long Island, drift-sand ridges extend along for a hun- 

 dred miles and vary in height from 5 to 40 feet. The coast of New Jersey, 

 down to the Chesapeake, and other coasts farther south, are similarly fronted by 

 sand-hills. Similar hills occur also on the east side of Lake Michigan, where 

 they reach a height of 100 to 200 feet; they are 215 feet high at Grand 

 Haven, and 30 to 93 near New Buffalo. In Norfolk, England, between 

 Hunstanton and Weybourne, they are 50 to 60 feet high. 



Such seashore driftings are a means of recovering lands from the sea. 

 The sea first makes the sand-flats or beaches, and 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 former estuary. 



The drift-sand also encroaches on fertile lands, forests, and villages. 

 Such regions of encroaching sands are called dunes. On Lake Michigan, as 

 Professor Winchell states, the sands are continually shifting with the 

 winds ; at Grand Haven and Sleeping Bear, the forest has become sub- 

 merged, and " presents the singular spectacle of withered tree-tops pro- 

 jecting a few feet above a waste of sands." The land at this place is 

 extending laJceward, through the wear and contributions of the arenaceous 

 shore rocks. Near Seven-mile Beach, on the New Jersey coast, in 1885, the 

 dune, 40 feet high, had encroached on a dense forest to such an extent that 

 " the tree-tops projected above its sands like the heads of drowning men 

 above the waves." (F. J. H. Merrill, 1890.) By such means, not only 

 bones, shells, tree-trunks, become the fossils of sand-heaps, but, in the 

 existing age, as in Egypt, even monuments, temples, and cities. 



1. Characteristics of ivind-drift or eolian formations. — The sands of wind- 

 drifts, although deposited by blasts of wind, make thin and regular layers 

 over the sand-fields and the surfaces of the rising ridges, producing a stratic- 

 ulate structure about as coarse as that of common alluvial clays, parallel 

 with the successive surfaces of the ridge. But such ridges are liable to 

 be cut off on one side or the other by the most violent of gales; and then 

 deposition from the winds goes on over a new outer surface. By repetitions 

 of such catastrophes, and continued depositions, the quaquaversal dip of the 

 wind-drift structure, represented on page 93 (Fig. 63), is produced. The 

 mode of formation and straticulate structure of sand-drifts is well illustrated 

 in snow-drifts, which are a result of like wind-drift action. As snow drifts 

 readily into heaps and ridges, wherever there is an obstacle however small, 

 so it is with sand. Flat or level surfaces are the exception in such regions. 



The drift ridges of coral sand or shell sand readily consolidate, and show 

 well the varying directions of the strnticulation, as at the Bermudas, 



