CHAPTER VI. 



THE BASIN OF THE THAMES. 

 (OxFORiisHiiiE, Beukshike, Bl'ckinghamsuiur, Heutfordsikue, Middlesex, Surrey, Kent, Essex.) 



IE Thames is not the largest river of the British Islands, but in 

 historical importance it has few rivals. The largest river of our 

 globe, the Amazon, drains an area of 2,300,000 square miles, but 

 within its basin there dwells not one tithe of the population which 

 crowds the great city of the Thames valley. True the city we 

 refer to is London, probably the greatest agglomeration of human beings which 

 the world ever saw. 



The river which flows past London rises within a short distance of the Bristol 

 Channel, on an ooHtic upland of the Cotswold Hills, which looks down upon the 

 broad plain of Stroud, Gloucester, and Cheltenham on the west. Some of its springs 

 rise close to the edge of the escarpment which faces the valley of the Severn, 900 

 feet below them. Formerly the whole of this upland region belonged to the basin 

 of the Severn, but continued erosive action has encroached upon the eastern slope of 

 the plateau, and for ages the water-parting has been travelling westward, the basin 

 of the Thames gaining in extent at the expense of that of the Severn.* An 

 examination of a geological map of England shows at a glance how extensively the 

 liassic strata in the region which gives rise to the head-waters of the Thames have 

 been reduced by denudation. 



The principal source of the river, known as Thames Head, rises at an elevation 

 of 37G feet above the sea, a little to the south-west of Cirencester. It gives birth 

 to the Isis, which, having been augmented by the Churn, the Colne, and other 

 streams, becomes navigable for barges at Lechlade, on the borders of Gloucester- 

 shire and Berkshire. Only after its junction with the Thame, in Oxfordshire, does 

 the combined river obtain its proper name of Thames, which it retains till it joins 

 the German Ocean. In its course it traverses various geological formations, 

 "which succeed each other with singular regularity. From the oolitic uplands near 

 its head it passes through a region of chalk, succeeded by tertiary rocks and the 

 alluvial deposits which surround its estuary. Speaking generally, the basin of the 



* Rams;iy, " Physical Geology and Gc^ography of Great Britain." 



