A HISTORY OF SURREY 



Putting aside for the present the consideration of the deep-seated 

 rocks, let us first examine the character and arrangement of the strata 

 which occur at the surface, since it is in these that we shall discover the 

 cause of its present configuration. The geological structure of the 

 county is so simple and its existing features depend so closely upon this 

 structure that it forms an ideal tract for the study of the elementary 

 principles of the science. 



As indicated by the different colours on the accompanying map, the 

 outcrops of the several geological divisions tend to form bands of varying 

 width running nearly east and west across the county, with the older for- 

 mations in the south and the newer in the north. This arrangement arises 

 from the general northerly dip or inclination of the beds, due to an un- 

 equal uplift of the land in past times by which the southern part of the 

 county has been raised to higher levels than the northern portion. Hence 

 we may walk east and west upon the same formation along the line 

 of ' strike ' from one end of the county to the other, while if we go 

 southward we soon cross to underlying, and if northward to over- 

 lying beds. 



For our present purpose it is sufficient to note that, as shown in 

 the section accompanying the map, this northerly dip prevails, with 

 some minor irregularities, throughout the greater part of the county. 

 We shall see later that it is dependent upon the presence of an elongated 

 dome of elevation which included the whole country between the 

 North and South Downs, having its axis a little to the southward of 

 our county boundary and extending through Kent and Sussex into the 

 eastern part of Hampshire. The central portion of this dome has 

 been so greatly eroded that it is now for the most part lower than the 

 sides, but at one time the successive belts of strata which now encircle 

 it have extended across it in a flat arch rising many hundreds of feet 

 above the highest ground now existing. The arch has been broken 

 through by long-continued erosion, and as some of the inner or lower 

 strata happen to be of less enduring composition than those by which 

 they were originally covered, the wasting away after the removal of the 

 higher portion has been more rapid towards the interior of the dome 

 than at the sides. 



Deep borings in Sussex and Kent have proved that immediately be- 

 neath the central portion of the dome there occurs a thick series of marine 

 deposits (Portlandian and Kimeridgian) of Upper Jurassic age ; but these 

 do not reach the surface. The oldest strata actually outcropping within 

 the uplifted tract consist of an estuarine series of shaly clays with thin cal- 

 careous stone bands, and with lenticular beds of gypsum in their deeper 

 portion. These ' Purbeck Beds ' cover a small area in Sussex some miles 

 to the south-eastward of the Surrey boundary. They pass upwards into 

 the ' Hastings Beds,' a thick series of soft sandstones and semi-coherent 

 sands, with intercalated bands of clay, apparently the sediments brought 

 down by a large river into a lake or estuary. 



