UNI7ERSI 



* r1 



EXCAVATING EFFECTS OF LAND-SPRINt 



deposit upon the sea "bed the stones they carried, or sometimes they 

 are drifted on shore, and the boulders there accumulate. During the 

 glacial period, when the British islands were at one time submerged, 

 multitudes of such erratics became stranded on the higher ground 

 as it emerged from the sea. But there are also evidences that icebergs 

 played a part in the formation of many geological deposits : large 

 blocks of granite have been found in the CJialk of Surrey, and 

 blocks of coal in the Chalk of Kent, and angular fragments abound 

 in the Cambridge Greensand, consisting of granijbe, mica schist, gneiss, 

 basalt, and a variety of felspathic rocks, hard sandstones, conglome- 

 rates, slates, and limestones, occasionally with indications of carbonife- 

 rous limestone fossils. Similar fragments are found in many of the 

 Oolitic rocks, especially the Portland limestone, and large blocks of 

 syenite have been recorded in the Coralline Crag. 



Springs. The precipitation of moisture on the surface of a country 

 is determined chiefly by the configuration of the land and the direc- 

 tion of the prevalent winds ; and hence high ground which rapidly 

 radiates its heat, and thus .condenses moisture out of the air, experi- 

 ences more torrent-like denudation than the lower districts of our 

 eastern and southern counties. But the character of the denudation 

 depends not only on the quantity of rain and inclination of the surface 

 over which it flows after reaching the earth, but also on the capacity 

 of the rocks to absorb the water. Thus Mr. Mellard Reade, treating 

 of the basin of the Thames, has estimated that of the rainfall of 27 

 inches 19 inches are absorbed by the porous rocks of the valley, and 

 only about 8 inches drain directly off the land to the sea; while in 

 regions of the more compact slate rocks of Cumberland and Wales, 

 where the rainfall is far heavier, only about 10 inches are absorbed 

 by the earth. But the water which is absorbed by the rocks passes 

 through them to emerge again at a lower level when it is charged with 

 various solids dissolved out of the porous beds. This underground 

 flow of water gives rise to the phenomena of springs, in which most of 

 our rivers take their rise. A spring may be defined as water flowing 

 from the rocks, which was originally absorbed as rain at a higher 

 level. Springs are classed into two kinds, commonly known as land 

 springs and perennial springs; for thermal springs and the intermittent 

 spouting springs termed geysers are varieties of perennial springs which 

 make a transition towards volcanic phenomena. 



Rain which falls on the surface of land where the subsoil is im- 

 pervious, is partly absorbed by the superficial earth, gravel, or sand, 

 and draining down the incline of the surface of the country, the water 

 flows out from the surface bed as a small stream, which is termed a 

 land spring. Such streams abound throughout the country, and 

 determine the existence of many small sheets of water and the village 

 ponds round which population has gathered. But not unfrequently 

 these streams make their way to the sea, and, where the destruction 

 of the cliffs is slow, produce, by their excavating power on the ground 

 they run over, those miniature valleys which in the Isle of Wight 

 are termed Chines, and are the Bunnys of Hampshire and Coombs of 



