On the Agricultural Geolorjy of England and Wales. 467 



skirting the lower or south-eastern slope of the great oolitic rano;-e, 

 are almost exclusively composed of fragments of oolite and chalk, 

 older pebbles being very sparingly intermixed. Examples occur 

 in Whittlebury-forest, Northam.ptonshire, and near Buckingham. 

 The flint gravel used for the repair of the road about Dunstable, 

 near the escarpment of the chalk, and which contains porphyry, 

 ivas identified by Dr. Buckland with that traced from Warvv^ick- 

 shire, along the valleys of the Thames, Cherwell, and Evenlode, 

 to London, and with that of the north midland counties described 

 by the Dean of LlandaiF. 



From Farcy's ' Report on Derbyshire,' it appears that frag- 

 ments of all formations, from granite to chalk, have accumulated 

 on the surface of all the strata which constitute the centre of 

 England. 



Review of the General Distribution of the Erratic Deposits north 

 of the Thames — Division into Upper and Lower Erratics. — 

 From the Scottish border to the Thames we have thus evidence 

 of marine action of very recent date over the whole of that part 

 of England and Wales, producing a great intermixture of local 

 and far-transported matter, in the form of gravel, clay, sand, and 

 boulders ; and we may be sure that the agencies which trans- 

 ported the coarser materials transported also much fine extrane- 

 ous matter, which has been mixed with that derived from the 

 neighbouring rocks to form the soil. 



The strike of the strata, which has given their direction to the 

 ridges of elevated land, influenced the distribution of the trans- 

 ported detritus. We have three lines of drift from the north-east : 

 that on the east of the chalk ridge, extending from Holderness to 

 Hampstead ; that between the chalk and the great oolite ; and 

 that west of the oolitic ridge. We have four from the west : that 

 of the Cumbrian erratics which have crossed the Penine chain ta 

 the German Ocean ; that of the Irish detritus lodged on the 

 western flanks of the Welch mountains, and that of the Lickey 

 quartz rock drifted eastward towards the oolitic ridge, and across 

 the Cotswolds, into the vale of London, We have also, in several 

 cases, indications, with a general drift towards the south, of a. 

 slight drifting northwards. These facts, including the last, are 

 quite in accordance with the motions of shore-ice, as described 

 in the polar voyages, influenced more by winds than by tides, and 

 sometimes moving, under this influence, in opposition to the 

 general current from the north. Such a general northern cur- 

 rent would also be subject to many local modifications, fi'om the 

 ridges of hills and mountains which would become groups of 

 islands and promontories, or submarine ridges, as the land 

 subsided. 



Every science furnishes instances during the early sta2:cs of its 



2 II 2^ 



