GEOLOGY 



latter resting on the Keuper Marl with gypsum. The patch of Chalky 

 Boulder Clay at Chellaston fills up an old valley and caps the hilltop. 

 It is of a sedimentary character, and has to a great extent escaped the 

 grinding character of the ice. 



The boulders range in age from Carboniferous to Cretaceous, and 

 the Carboniferous rocks have been derived from the Older Pleistocene 

 Boulder Clays. East of Chellaston the great Chalky Boulder Clay is not 

 met with again till we come to the ridge between south Notts and 

 Leicestershire. 



In Derby a patch of stratified gravel with flints was seen in an 

 excavation in Green Lane. It probably belongs to the Chalky Gravel 

 stage, as does also another patch near the Arboretum. On Chellaston Hill 

 the Chalky Boulder Clay is capped by a deposit of gravel at least 17 feet 

 in thickness and covering an area of about a quarter of a square mile. 

 A section of this sand and gravel may be seen between Chellaston and 

 Weston. The sand contains flint and quartz pebbles. On the high 

 land south of Ashbourne gravel is of tolerably frequent occurrence, in 

 most cases the deposit is very much disturbed and signs of stratification 

 are only shown in the lower parts of the sections. 



The deposits of Newer Pleistocene age indicate the first signs of 

 subaerial erosion and the consequent formation of river gravel. During 

 this stage the rivers cut down their valleys through the older Boulder 

 Clays and sands to within about 20 feet of their present depths and left 

 their gravels stranded as terraces at various heights above their present 

 courses. Upon these gravels there frequently rests a Boulder Clay which 

 is conformable to the surface features produced by the erosion of the 

 previous stage. 



The erratic boulders distributed over the westerly part of Stafford- 

 shire are considered by Mr. Deeley to belong to this stage and to prove 

 that the climate was sufficiently severe for the Scotch and Cambrian 

 glaciers to invade the western portion of the Trent basin. 



The interglacial river gravel occupies terraces at various heights 

 along the valley of the Trent and its tributaries. In the valley of the 

 Trent between Findern and Weston there are long patches of high level 

 river gravel, which by their oblique bedding indicate currents down the 

 valley. A lower terrace may be traced from near Weston to within 

 about half a mile of Aston, and a still lower series of terraces occupies 

 considerable areas in the valleys of the Trent and Derwent. One of these, 

 a large crescent shaped terrace, stretches from Willington to Stenton 

 Lock. Its escarpment runs along the north side of the Trent valley past 

 Swarkestone, Weston, Aston and then up the valley of the Derwent 

 past Elvaston and Osmaston to Derby. Posterior to these river gravels 

 is the later Pennine Boulder Clay which is well developed in south 

 Derbyshire. Wherever the rocks upon which this clay rests are exposed 

 they are seen to be contorted. Mr. Deeley considers that the contortions 

 have been formed by the same ice sheet that produced the later Pennine 

 Boulder Clay, and that the direction in which the ice sheet moved is 



