GEOLOGY Oxford Clay Cornbrash Great Oolite Upper Estuarine Beds (none on this alone r) Lincolnshire Oolite Northampton Sand Upper Lias Middle Lias Lower Lias Pervious 8 79 27 102 49 265 The significance of these figures will be better appreciated by look- ing at the areas covered with each formation on the map. Some villages occupy parts of two or more formations, such are classed as on pervious ; others may be on Drift yielding water although classed as on impervious, for they all get water somehow ; and of course different observers might arrive at slightly different results from these causes. Other results naturally followed the selection of dry sites on pervious beds. These water-bearing beds furnish the only ready-made building material in the county, and if we eliminate the newer brick buildings of villages and towns, the districts covered by the thicker pervious rocks — Great Oolite to Middle Lias — show the fact in their buildings. WATER SUPPLY As villages grow into towns the individual provision of water by contiguous springs or local wells tends to give place to public works on an extensive scale. The first device that suggests itself, and one that has been carried out in a number of cases, is to tap one of the water-bearing beds at a considerable depth by digging or boring through the superin- cumbent rocks in the direction of dip of the beds. The water so tapped is likely to be very pure organically, because it has passed through such a mass of filtering material from the place where it got in, often many miles away. For the same reason it is equable in temperature, does not fluctuate with the seasons, and providing no more is pumped out than gets in naturally over the catchment area by percolation, is permanent. The water tapped in a porous bed between two impervious ones is a transtratic springs and as it usually rises considerably in the bore-hole or well, this is called an artesian well. Where such a method is im- practicable, or where the yield by it is insufficient, as has occurred at Northampton, Kettering, etc., reservoirs have been constructed to catch, not far from their source, a number of springs draining a considerable area, by throwing a dam across the valley where the resultant stream seeks to discharge. The Trias furnishes the deepest source of water so far tapped within the county. The water is very salt, containing from 1,200 to 1,500 37
