SUCCESSION IN THE TRENT BASIN. 475 



to pebbles and boulders of local rock, flints aud granite. In the 

 Cemetery itself an excavation passed through reddish Boulder- clay 

 containing masses of sand with shell-fragments. In an old pit close 

 by the Boulder-clay rests upon shelly sand over which it has been 

 forcibly thrust. 



Where the Chalky Gravel rests upon, or has been formed in the 

 immediate vicinity of, Chalky Clay, it contains numerous large 

 boulders derived from that deposit. In Staffordshire they are much 

 more scarce in the Chalky Gravel, the erratics mentioned by Mr. 

 Mackintosh belonging, almost without exception, to the Later Pennine 

 Boulder-clay. With regard to this point the Rev. W. S. Symonds 

 remarks*, " I have observed one peculiarity as regards this sand and 

 gi'avel and fossiliferous drifts in several localities, as near Wolver- 

 hampton, near Shrewsbury, and in Yorkshire : it is that they often 

 have large boulders lying immediately above them, or on their 

 upper surface, as if the boulder erratics had been deposited after the 

 accumulation of the shell-bearing sands and gravels." This state- 

 ment describes their general mode of occurrence, the Chalky Gravel 

 with its boulders and pebbles having been formed by the marine 

 denudation of the Chalky Clay, and the Later Pennine Boulder- 

 clay, with its large erratics, by the glaciers which entered the Trent 

 basin from the surrounding mountainous districts to the north and 

 west. 



South of Penkridge about five feet of highly contorted sandy 

 Boulder-clay rests upon disturbed red marl. Boulders are numerous, 

 many of them of rocks entirely foreign to the district. 



A stone-quarry near Brewood Parm, excavated in Keuper sand- 

 stone, which here contains footprints of Lahyrinthodon^ shows the 

 upper five or six feet of red marl mixed with pebbles and sand and 

 converted into a morainic clay. 



Not far from Penkridge another interesting exposure may be 

 seen. Pebbly sand or clay, three or four feet thick, here covers red 

 marl, which in its turn rests upon beds of massive fine-grained sand- 

 stone. Below the red marl the sandstone layers are violently 

 disturbed and broken, the red marl being thrust into the crevices 

 between the displaced blocks. It is evident from the section that 

 the disturbing force passed over a surface whose contour corre- 

 sponded very nearly with the present one, the modern streams having 

 only excavated shallow valleys through the old glaciated surface. 



Between Penkridge and Staff'ord the only exposure I am aware 

 of is the one at Ash Flat, mentioned by Mr. Mackintosh. The 

 section shows about seven feet of reddish Boulder-clay. I was in- 

 formed that for three or four feet beneath the usual working-depth 

 it is more stony and rests upon sand — probably Chalky Gravel — 

 from which the water rises in powerful springs. The clay contains 

 intruded masses of sand, and besides pebbles of quartz, quartzite, 

 sandstone, &c., a few flints may be found. 



All these sections, occurring as they do immediately to the west 

 of the South-Staff'ordshire Coal-field, should contain, if they belong 

 * 'Records of the Eocks.' 



