264 



PHYSICAL GEOGRAPHY. 



mountain limestone of England, through the fissures of the rocks, produced in the course 

 of the consolidation and shrinking of the mineral masses. They seldom appear, however, 

 on the sides of limestone hills, but break out in great numbers, and often with extraordi- 

 nary impetuosity, around their bases. In other conditions of the surface, the water per- 

 colates through the masses of sand, gravel, or chalk, that compose it, till it meets the solid 

 rock, or a bed of impervious clay, which arrests its further descent, and springs are then 

 formed at the point of the lowest level, on the edge of the rock or clay that dams it up. 

 With few exceptions, the lower beds of the chalk formation are completely saturated with 

 water which has percolated through the superior strata to the base, where its downward 

 course is stopped by a subsoil of blue clay, which occasions the accumulation in the lower 

 regions of the chalk, and the springs and rivulets which issue near the foot of every chalk 

 hill. It is more difficult to account for springs where the country is neither hilly nor 

 uneven, but constitutes a great level or plain. The water in these instances reaches the 

 surface by ascension, or flows in a direction contrary to that produced by the force of 

 gravitation. There can be little doubt, however, that many of these springs derive their 

 supply from distant elevations, and are produced by the natural tendency of liquids to 

 find their level. Other examples are perhaps due to capillary attraction, in consequence 

 of which water ascends through the pores of the earth in the same manner as it rises in 

 capillary tubes in sponge or sugar-loaf so long as the latter remains undissolved. 



In order to give a distinct though general view of the curious and complicated pheno- 

 mena of springs, they may be advantageously considered under different heads. 



1. Perennial. Some springs are 

 ever-flowing, and answer to the 

 expression of sacred poetry the 

 " fountains of living water." They 

 do not dry up during the longest- 

 continued drought, and suffer little 

 or no diminution in their volume. 

 These are obviously quite inde- 

 pendent of the last showers that 

 have fallen, though their supply 

 mav primarily proceed from the 

 rain and melted snow. It is rea- 

 sonable to suppose that they gush 

 from a body of water collected in 

 subterranean cavities, so vast as 

 not to be drained off by the con- 

 stant stream during the most pro- 

 tracted season of dry weather, be- 

 fore the interior basin is reple- 

 nished. Of this nature is the 

 celebrated spring of St. Winifred, 

 at Holywell, in Flintshire, one of 

 the finest in the world, which ap- 

 pears to be situate at the point 

 where the limestone first comes in 

 contact with the coal measures. 

 The quantity of water thrown up 



ot. vv milieu VT en. 



is estimated at eighty-four hogsheads, or twenty-one tons, in a minute. 



been known to fail, but is subject to reduction during drought. The stream never 



St. Winifred's Well. 



