ALLUVIUM. RECENT FORMATIONS. 775 



sea upon the piers of the bridge of Caligula, giving the same amount of subsidence 

 yearly. 



Vertical movements, of elevation and subsidence, appear to be physical events of 

 modern date in the history of the Isle of Wight. In the reign of James I., during an 

 attempt to drain Brading Haven, a well was discovered near the middle, cased with stone, 

 proving that the site had once been dry land, upon which man had planted his foot, and 

 probably reared his habitation. This may be explained without recurring to an actual 

 subsidence, by supposing the Haven to have been a low-lying level, protected from the 

 ocean by a mound, through which the sea broke and took possession of the soil. But Sir 

 Richard Worsley, in his history of the island, mentions the following particulars: 

 " Looking eastward from the elevated spot (St. Catherine's Hill) where the tower stands, 

 two other hills are to be seen ; the nearest, which is about three miles distant, is called 

 Week Down, over which, about a mile and a half farther, appears that called Shanklin 

 Down, or Dunnose Head. Concerning these downs a singular circumstance is remarked 

 by the inhabitants of Chale, of which the evidence seems unobjectionable. Shanklin 

 Down may now be guessed to stand about a hundred feet higher than the summit of 

 Week Down ; yet old persons, still living, affirm that within their remembrance Shanklin 

 Down was hardly visible from St. Catherine's : they declare, moreover, that in their youth 

 old men have told them they knew the time when Shanklin Down could not be seen from 

 Chale Down, but only from the top of the beacon, the old post of which stands near the 

 chapel. This testimony, if allowed, argues either a sinking of the intermediate down, or 

 a rising of one of the other hills." However dubious we may be as to the foundation of 

 this record, the evidence of such physical changes having occurred in recent times 

 appears in every quarter of the globe, the raised beaches proving the instability of the 

 level of land and sea, and the change of level to have been occasioned by a real displace- 

 ment of land. On the banks of the Frith of Forth, near Burrowstowness, there is a bed 

 of marine shells several feet in thickness, extending about three miles in length, now 

 situated many feet above the level of the waters of the Forth. Elevated beaches appear 

 along the west coast of South America, showing successive uprisings of the land the 

 effect of the earthquakes that have so frequently acted upon that part of the continent. 

 By the catastrophe of Feb. 20. 1835 the land round the bay of Conception was perma- 

 nently upraised two or three feet ; and the elevation was much greater in other places ; 

 for Captain Fitzroy, about thirty miles distant, found beds of putrid muscle-shells still 

 adhering to the rocks, ten feet above high-water mark, where the inhabitants had for- 

 merly dived at low-water spring tides for these shells. 



3. Lacustrine shore silt ; marls, calcareous, siliceous, and aluminous. 



Lakes, receiving a considerable river or many small runlets, act as settling pools to the 

 dissolved or suspended matters conveyed into them from the adjacent districts, the waters 

 running off through their natural outlets in a filtered condition. The debris brought into 

 them consists ordinarily of fine particles ; but heavier sediments are introduced when the 

 streams are in flood, and the transported material will be deposited in the bed of a lake 

 at a greater or less distance from the point of entrance, according to the force with which 

 the waters from the land rush into it. Where a lake has a considerable expansion, so that 

 the winds act powerfully upon it, producing strong waves, a portion of the foreign matter 

 is washed up upon the shores, forming beaches of silt and shingle, as in the bays of Lake 

 Superior. The immense reservoirs of fresh water in North America present several 

 instances of the phenomenon of raised beaches, appearing one above another, like the 

 seats of an amphitheatre, at some distance from their present shores. Seven of these have 

 been remarked near Cabot's Head on lake Huron ; the highest overgrown with spruce 

 firs, the next covered with trees and bushes of a smaller kind, the third with shrubs and 



