GEOLOGY known as ' crowgold,' but is nowhere present in the county in suffi- cient quantity to be of commercial value. The stratum plays an impor- tant part in connection with the water-supply of the district. The argillaceous character of the middle portion renders it partially impervious to water, so that at its junction with the overlying porous portion numerous springs arise, which however are now fewer in number and smaller in volume than they were some twenty years ago. This feature was strikingly exemplified during the excavation of the extensive cutting at Chalton, the flow of water in the Chalk Marl being so copious that in driving a heading into the escarpment the workmen had to wear miners' costume, as their clothing was in a state of constant saturation. The Chalton cutting is the only exposure of the bed of any importance in the county. A sandy layer near its base is not exposed here. The Totternhoe Stone takes its name from the village of Tottern- hoe about three miles west of Dunstable, where it attains its maximum development which does not exceed 22 feet. Away from this locality it rapidly diminishes in thickness. It is a dark grey, slightly arenaceous, compact limestone, with a peculiar grain to which the term * curly ' is applied by the quarrymen. The comparative coarseness of the materials of which it is composed, and the presence of siliceous particles, indicate that there was a temporary increase in the force of the currents which effected its deposition, over those which prevailed during the era of the Chalk Marl. Scattered irregularly through it are numerous dark brown amorphous masses, and at its base there is usually a layer of green-coated phosphatic nodules; a further indication of current-action. Many springs arise from it at the foot of the Dunstable Downs and elsewhere. Totternhoe Stone was formerly extensively employed in local archi- tecture, numerous churches in the south of the county affording examples of its use, but it is not sufficiently indurated to withstand for any great length of time the climatic changes to which it is subjected when used for exterior decoration. It weathers badly, as may be seen from the present condition of the west front of Dunstable Priory Church. 1 It is much more suitable for interior work ; but even for this it has long been superseded by more durable materials brought from a distance. The numerous and extensive relics of excavations on Tottern- hoe Hill show that this stone has been quarried for a very long period. Until about the middle of the nineteenth century it was customary to construct tunnels which commenced at the outcrop of the stone and were carried a considerable distance into the hillside. In later times tramways were used to bring the material to the surface, the incline, correspond- ing with the dip of the bed, being only slight. This system was then superseded by open quarrying, the whole of the overlying bed of Lower Chalk being removed and used for making lime. This method of working terminated during the last decade of the nineteenth century, consequent upon the cessation of the demand for the material. 1 This is now undergoing restoration, the material employed being a Bath stone. 1 17 3
