Tin-: KMCKNK SKI; IKS 541 



much smaller .-pare than tin- London Clay because they have been 

 removed lYmn tin- ^ivah-r part ..f it- >tirl'ai-e by subsequent detrition 

 and enxion, but there is good reason to believe thai tin y \\rie not 

 only rne.\ten>ive with the London Clay but spread beyond its 

 original borders. The chief remaining tract of Bagshot Saud is an 

 area about 24 miles in length with a breadth of about 10 or 12 

 miles, and occupying parts of Berkshire, Hampshire, and Surrey. 

 Aldershot, Farnborough, Bagshot, Wokinghain, Ascot, and Cobham 

 all lie within this area. Westward there are several outlying 

 tracts, some large and some small ; and north of the Thames in 

 Middlesex are three small outliers capping Harrow, Hampstead, 

 and Highgate Hills (see Fig. 183). 



The extreme thickness of these sands in the Bagshot and 

 Farnborough country is from 130 to 150 feet. Westward at 

 Ramsdell, in the outlier between Basingstoke and the valley of 

 the Kennet, there is a bed of brown clay very like London Clay, 

 and 30 feet thick, in the lower part of the Bagshot Sand. 



In the Hampshire Basin the Bagshot Beds consist of bright 

 yellow and white sands with bands of grey laminated sand and clay 

 and (in the upper part) layers of white pipeclay, which contain 

 leaves and stalks of plants belonging to the genera Aralia, 

 Ccesalpinia, Comptonia, Dryandra, Ficus, Laurus, Quercus, and 

 other Dicotyledons. Ferns are rare in the Isle of Wight, but 

 Chrysodium lauzeanum abounds at Studland in Dorset. This flora 

 indicates a warmer climate than that of the Reading Beds. 



There is much difference of opinion as to the thickness assign- 

 able to these beds in the Alum Bay section (Fig. 185) ; the Geological 

 Survey classes all the sands and clays which do not yield marine 

 fossils as Lower Bagshot, and these amount to 662 feet. Mr. J. S. 

 Gardner, 4 however, has shown that the special Bagshot flora does 

 not occur above the pipeclays, and that the higher beds at 

 Bournemouth contain a very different flora. He also thought that 

 the lower part of these sands replaced the upper part of the London 

 Clay, but if the latter is restricted to 233 feet, the Bagshot Sands 

 will have a thickness of 243 feet at Alum Bay, and decrease east- 

 ward till they are only 98 feet in Whitediif Bay. 



At Studland and Corfe in Dorset the Bagshot Beds have the 

 same facies, but westward they pass into coarse subangular gravels, 

 which near Dorchester overlap both London Clay and Reading 

 Beds so as to rest directly on the Chalk. These gravels contain 

 pebbles of Cretaceous flint and chert, I'nrbeck marble, with many 

 of quartz and of Palaeozoic rocks probably derived from the 

 Permian breccias of Devonshire. Still farther west they overstep 

 the Chalk and rest on the Selbornian Sands. 



