derange: underground water-supply and river floods. 215 
with porous material, and do not offer any obstacle to the passage of 
of water, and it is only wlien the Keuper rocks are either present, or 
have been just overhead, but since removed by denudation, that the 
faults form into barriers. 
The Yorkshire oolites form a valuable source of pure under- 
ground water, while the Yorkshire chalks offer an area of absorption 
of no less than 420 square miles, and has been carefully studied by 
Mr. J. R. Mortimer. A considerable area of oolitic rocks occur in York- 
shire, and their exceedingly permeable character causes them to 
absorb a very large proportion of the rainfall, which charges the 
pores and fissures with immense volumes of water of an average hard- 
ness of 23 •52 grains per gallon, but capable of being softened at a 
moderate cost to o"8. Vast stores of magnificent water are thrown 
out in springs of very large volumes, which are seldom used by com- 
munities until it has found its way into rivers, and becomes 
polluted. The temperature of these springs ranges from to 11°8. 
The proportion of organic matter yielded to dumb- wells in this 
formation is exceedingly small, proving the Oolitic Rocks are not 
inferior to the New Red Sandstone in the energy with which they 
oxidize and destroy the organic matters present in the water percola- 
ting through them, which becomes bright, sparkling, palatable, and 
perfectly wholesome. 
The alternating character of the Oolitic Rocks of Yorkshire have 
had an important bearing on the selection of the sites of villages,, 
thus Mr. Fox-Straugways* remarks that " on either side of the great 
clay valley, where springs of beautiful calcareous water bursts out, 
are on the north, the villages of Witton, AUerston, Ebberston, Stain- 
ton, Brompton, Wykeham, Hutton, Buschel, Ayton, and Seamer ; 
and on the south those of Riilington, Thorp Basset, Wintringham, 
Heslerton, Sherburn, Ganton, Flexton, Folkton, Hunmanby, and 
smaller hamlets. 
The chalk absorbs the largest proportion of the rainfall of any 
rock''', yielding it in deep wells in a condition of purity from organic 
matter unsurpassed by any other geological formation, and it consti- 
tutes a vast underground reservoir in which the water is not onlj^ kept 
* Geol. Sur. Mem. On the country around Scaiboro' and Filey. 
