512 PLEISTOCENE AND RECENT. 



Weybridge,' at Trumpington near Cambridge, and many other places.^ The 

 pebbly clay at Shooter's Hill, which in Mr. Goodchild's opinion was disturbed by 

 Glacial action, is a similar instance.^ Nor are these surface-contortions confined 

 to Pleistocene deposits. The Chalk, where exposed at the surface in the valleys of 

 the Yare and the Wensum, not unfrequently shows signs of disturbance ; the flint- 

 layers are broken up, sand and stones are introduced, and the Chalk itself presents 

 a rubbly appearance, to a depth of from i to 8 feet, and sometimes more. This 

 disturbed Chalk is often spoken of as the "Glaciated Chalk" ; it passes gradually 

 down into the undisturbed Chalk beneath. (See p. 421.) " Pipes" are abundant 

 in it, and at Trowse it is burnt for lime, being considered to furnish better material 

 than the undisturbed Chalk. Near Brandon it is known as 'dead loam.' In some 

 cases the appearances may be due to the influence of the ice which formed the 

 Chalky Boulder Clay ; but in other cases the agent was of subsequent date. 

 Remains of Mammoth and Red Deer have been met with in the disturbed Chalk 

 near Norwich.* 



The Lower Greensand at Great Hazeley in Buckinghamshire presents evidence 

 of apparently similar surface-disturbance,* and this is sometimes to be seen in 

 superficial beds of the Oolites. We have also the evidence of the Terminal 

 Curvature of slaty rocks to show that these surface disturbances may have been 

 produced at different dates. (See p. 494.) Surface disturbances moreover may 

 in some cases be produced by the slipping of superficial accumulations or of the 

 'soil-cap ' down the slopes of hills, a process analogous to landslips.'' (See sequel.) 



ALLUVIAL DEPOSITS. 



The deposits of ]\Iodern rivers, lakes, and estuaries may be 

 classed under the above heading. They comprise gravel, sand, 

 brickearth or loam, clay, mud, and silt ; peat, too, may be included, 

 as it is formed in swamps along the borders of rivers, and may 

 occur interstratified with other materials in fluviatile, lacustrine, or 

 estuarine deposits. These Alluvial or Valley deposits are some- 

 times broadly divided into (i) Alluvium, being the latest sediments 

 deposited by the river; and (2) Brickearth, Gravel and Sand, 

 which, as a rule, occupy higher levels in the valley than the 

 Alluvium, although they often form part of it. 



Brickearth. — This consists of loam, a mixture of clay and sand in varying 

 proportions ; in general it is of a brown colour mottled with red, and it is largely 

 used for brickmaking. 



Gravel. — The Caravels that are met with in our river-valleys, and which are 

 evidently connected with similar areas of drainage, occupy various elevations with 

 respect to the level of the present rivers and streams. This is natural, for they 

 represent different stages in the excavation of the valleys, the beds at a higher 

 level being older than those at a lower level. Thus in some instances it is found 

 convenient to group the deposits as follows : — 



Low-level Valley gravel. (Alluvium.) 

 High-level Valley or Terrace gravel.'' 



1 Hudleston, Q. J. xlii. 170. - See J. Allen Brown, P. Geol. Assoc, viii. 173. 

 3 P. Geol. Assoc, ix. 151. * Geol. Norwich (Geol. Surv.), p. 137. 



5 See also Fitton, T. G. S. (2), iv. 276. 



^ See also R. W. Coppinger, Q. J. xxxvii. 348, and F. C.J. Spurrell, Rivers 

 and Denudation of West Kent, 1886, p. 30. 



■' The term High-level gravel has been applied to Glacial deposits. 



