Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/301

1870.] WILSON RUGBY SURFACE-DEPOSITS. 193 towards the N.N.W. The heights of points nearly equidistant along the Hillmorton, Dunchurch, and Avenue roads are in succession 403, 400, 400, 400, 392, 375, 370 feet above the sea, indicating a slope westward, while the heights 396, 382, 378, 355, on the Dunchurch, Rugby, and Clifton roads, indicate a still more decided slope towards the north.

The southern edge of this plateau is well defined. The northeastern edge, which forms the southern flank of the Avon valley, is less regular, though nearly equally steep. It is broken by a succession of lateral valleys which contain tributaries to the Avon. The village of Lowmorton occupies such a lateral valley; another is crossed by the Lowmorton and Rugby road ; and an important valley is crossed at the Victoria works near Rugby, and by the Bilton road between Rugby and Bilton.

Nature of the subjacent Strata.

The whole of the district under examination is Lower Lias, with the exception of a few patches of Middle Lias towards the southeast. The limestones and clays of the Lower Lias are well developed, and abundantly exhibited in large lime- and clay-works ; and an admirable section of them has been the only profitable result of an artesian well of 1145 feet depth. The lie of the hills and valleys appears to be totally independent of the distribution of the clays and limestones ; the limestones do not form the escarpments, nor do the clays determine the paths of the rivers ; the geological skeleton and the actual contour have no obvious and immediate connexion with one another.

Detailed Account of the Surface-deposits on the Rugby Plateau.

At Bourton the soil is generally gravel and sand like that at Rugby, 12 or 13 feet in thickness, reposing on clay. At about 30 feet depth the limestone rock is reached. This, as is pretty obvious from an inspection of the map, and a knowledge of the general strike of the strata, is the continuation of the Newbold limestone, and it does in fact come to the surface at the foot of the escarpment at Draycote, immediately below Bourton. One well at Bourton is 90 feet deep, 60 feet of it being in the rock.

The same general character continues along the escarpments to Thurlaston, which village rests on gravel of the same or greater thickness. In two places, however, there arc wells 50 deep feet, which of course indicate that the depth of the gravel there is insufficient to supply the surface-wells with water. At Thurlaston the limestone rock is not reached ; somo thin bands of it which lie interstratified with the clay are passed through.

At Dunchurch the surface-deposits are precisely the same. I have not been able to hear of any deep wells. The gravel and sand are generally about 13 feet deep. At Mr. Harrison's house, on the brow near Bilton Grange, there are three wells — two in gravel, of 13 and 14 feet, and one in clay, of 30 feet. At Bilton Grange the depth of