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 A HISTORY OF RUTLAND ward. It may be useful therefore it we indicate how the water gets into the Inferior OoHte, how some of it is thrown out in the form of springs, and how the rest flows eastward to serve as an underground reservoir for the towns and villages along the border of the Fenland. A large part of the rainfall is absorbed by the sands and limestones of the Inferior Oolite, for not only is much rain absorbed directly it falls on the wide areas over which this formation is exposed, but much of that falling on the Great Oolite runs off till it reaches the Lincoln- shire Limestone into which it quickly soaks. The runnels which carry the rain off the slopes of the Upper Estuarine clays often terminate in a swallow-hole at the junction of clay and limestone ; these holes are some- times open rifts, but more often are funnel-shaped depressions opening downwards into underground passages which have been made by the widening of the joints and fissures in the limestone. In some cases a large volume of water is thus carried off, and after heavy rains the noise of its descent into the swallow-hole can be heard for some distance. The same is the case with the water which runs off the tracts of Boulder Clay lying on the area of the Limestone. Even where water runs over the Limestone for a little distance it often disappears suddenly and joins the subterranean streams, but in a few cases it comes to the surface again lower down the watercourse; thus the brook which rises at Market Overton (a tributary of the river Witham) disappears near Thistleton to issue again above South Witham ; the same is the case with the river Glen between Little Bytham and Careby just outside the limits of Rut- land. It is probable also that the streams which rise on the Liassic area contribute some portion of their volume to the stores of the Inferior Oolite by leakage along their channels as they flow over the Limestone to join the Welland. Thus in various ways a large quantity of water enters the combined mass of the Northampton Sand and the Lincolnshire Limestone and makes its way downward toward the base of the forma- tion. Of the water thus absorbed a portion is thrown out again in the form of springs along the boundary of the Northampton Sand and all round the outliers of this sand, because it cannot sink into the impervious clays of the Upper Lias. It is these springs which have determined the sites of most of the villages in this part of the county. Some of the water thus issuing is hard and deposits calcareous matter (tufa or travertin), having dissolved much carbonate of lime in its underground course; some are chalybeate springs, having dissolved iron from the iron- stone beds, and a few of the latter, such as that in Burleigh Park near Oakham, were noted as ' spas ' in former days. But the greater part of the water which is absorbed by the Lincoln- shire Limestone passes eastward, because the beds are inclined in that direction, and as it cannot sink below the base of the Northampton Sands nor rise above the top of the Limestone where that is continu- ously covered by the Upper Estuarine clays, the water level in the M