XVII.] GEOLOGY OF THE THAMES BASIN. ^^^ 



or along with the extinct mammalia ; but are confined to the 

 most superficial deposits, and to the present level of the 

 river. That period in which man was in the habit of using 

 implements exclusively of stone is known to antiquaries as 

 the stone age; and Sir John Lubbock has distinguished the 

 early part of this period, in which unpolished stone was in 

 use, as \\\& palcEolithic'^ age, and the later period, when man 

 had advanced to the stage of grinding and polishing his 

 weapons, as the neolithic'^ age. Fig. 85 represents therefore 

 a palaeolithic, and Fig. 86 a neolithic implement. 



All the deposits hitherto described in this chapter — such 

 as the gravels and brick-earths — consist of loose materials 

 distributed in patches, more or less extensive, over tbe 

 surface of the solid rock. Hence, they are classed together 

 by the geologist as "superficial deposits;" and are not 

 represented on a geological map, unless the map be con- 

 structed for the special purpose of exhibiting the surface- 

 geology, as in the case of the little sketch-map. Fig. 81. 

 An ordinary geological map shows, in fact, the kind of rock 

 which would be exposed on the surface of the ground, if the 

 superficial deposits were removed. In some cases, there 

 are no deposits of this kind, and then, of course, the actual 

 rock of the country is exposed. The map of the basin of 

 the Thames given in Plate V., is coloured, in such a 

 manner, as to show what rocks would be seen on the face 

 of the country, if it were not obscured by gravels, loams, 

 and other superficial accumulations. 



The small areas of light brown tint in Surrey and Berks 

 represent the highest, and therefore the newest, beds within 

 the Thames basin. They are well seen in the sandy tracts 

 of Bagshot and Ascot Heaths ; and, from the former of these 



^ Pahtolithi-, from n-aAaio'?, pal rios, old ; Xidoi, lillios, stone. 

 2 Neolithic, from vios, ncos, new. 



