182 D. MACKINTOSH ON THE DRIFT-DEPOSITS 



time possible that the river in preglacial times may have been chiefly 

 occupied in deepening its channel, and that the process of widening, 

 by lateral undermining, may have chiefly occurred in interglacial and 

 postglacial times — in other words, after the accumulation of the 

 high-level drifts. 



Redistribution of Triassic Pebbles. 



It is well known that south and south-east of the Wrekin and 

 Ashley waterparting (as well as around the waterparting itself) 

 there are extensive Triassic pebble -beds, which have been broken up 

 and redistributed in a S. and S.E. direction, probably for the most 

 part by oceanic currents and waves ; for it would be unreasonable 

 to suppose that all the great and often continuous spreads of pebbles 

 could have been uprooted and transported by floating ice. Along with 

 Scottish, Cumbrian, or Welsh erratics, they may be seen imbedded 

 in clay, loam, or sand at least as far south as Bromsgrove*. Their 

 distribution must therefore have taken place during a part, if not 

 the whole, of the period of the great northern boulder-dispersions. 

 It is worthy of remark that in the neighbourhood of the lower course 

 of the Severn many sections of so-called drift consist of Triassic 

 pebbles in situ. A notable instance of this may be seen in Spring- 

 Hill gravel-pit, between Bewdley and Kidderminster, which contains 

 no drift belonging to the glacial period excepting a few local fragments 

 on the surface and the harder parts of limestone burnt for manure (?). 

 It is likewise worthy of remark that many published sections of 

 quartzose and flinty gravel are calculated to mislead, because their 

 details show no greater changes of conditions during their accumu- 

 lation than often take place in a few days on a sea-beach subjected 

 to alternate denudation and deposition. 



Drift-deposits of the East-Midland Counties. 



As may be gathered from my former paper, the area between 

 "Wolverhampton and Stafford may be regarded as the meeting- ground 

 of erratics from the TsT.Ii.W. and of erratics from the E.JST.E., the 

 former chiefly granite and felstone, and the latter chiefly Cretaceous 

 and Jurassic debris. Over this meeting- ground both sets of erratics 

 would appear to have been precipitated into a drift-matrix resulting 

 from a submergence which extended round the Pennine hills from 

 the source of the J^.IST.W. erratics to the source of the E.IST.E. erratics. 

 Prom the area between Wolverhampton and Stafford the deposit 

 with Cretaceous and Jurassic debris (after losing its erratics from 

 the JS'.IST.W.) extends over the east-midland counties until it gra- 

 duates into the Challcy Clay, thus rendering it probable that the 

 Chalky Clay is on the same horizon with the deposit containing 

 erratics from the N.N.W. between Wolverhampton and Stafford. 



* Besides large boulders, I saw many pebbles of Arenig felstone imbedded, 

 along with Triassic pebbles, in loamy clay or sand betvTeen Hagley and Catshill. 

 Mr. Ampblett, of Olent, tells me that these drifts are sometimes separated from 

 the underlying rock by a distinct line of demarcation. 



