THE STORY OF SOME PEBBLE HILLS 77 



a rarity here. The pebbles are quite curving dome or hummock of chalk, 

 round, spheroidal even, save for a Myriads of microscopic siliceous par- 

 flattening above and below. A large tides, held in solution throughout the 

 proportion of the stones are filled with chalk ocean, aggregated around sponges 

 little depressions, lined with white, and other organisms, forming lumps 

 These hollows are caused by the removal of curiously shaped flint. Contem- 

 of the soluble variety of silica in the poraneously with this process, and 

 flint, a process accompanied by loss of again after the chalk was raised, there 

 colouring matter. Using a pocket lens, was a general movement of the dis- 

 we see that the surface of each pebble seminated silica towards the joints 

 is battered and minutely hackled in and cracks in the chalk, resulting in 

 all directions by a network of cracks, the deposition of the long, dark bands 

 These are incipient conchoidal frac- of flint which decorate quarries hewn 

 tures, typical of a flint which has in the Upper and Middle Chalk, 

 been smartly struck. The pebbles, Once lifted above the surface, the 

 then, have been subjected to unnum- chalk was attacked by frost, rain, and 

 bered blows and buffetings. Now and streams. The carbonate of lime was 

 again we see a heap of the flints eaten away, and carried off invisibly, 

 cemented into a conglomerate or The insoluble silicate of alumina re- 

 pudding-stone, by the aid of rufous mained, interspersed with warty 

 iron oxide and a little carbonate of knobs of flint. Before the flint was 

 hme. exposed, however, there was laid down, 

 In the secondary, or Mesozoic epoch in a Tertiary sea towards the north, 

 of the earth's story, there was de- those buff-coloured Thanet Sands which 

 posited, in a moderately deep, warm, underlie our pebble bed. These sands 

 tranquil ocean a " chalk drizzle " of contain scarcely a pebble, hence the 

 tiny foraminifera ; broken tests of sea great erosion of the chalk had not 

 urchins, molluscs, and sponges, to- yet begun. Soon, indeed, the clayey 

 gether with the creatures themselves, residue of the destroyed chalk, with 

 denizens of the waters. This calcare- sands gnawed from older rocks, were 

 ous sediment, vast in age and thick- washed down into a series of lagoons 

 ness, was consolidated, and ultimately or a large irregular estuary, fringed 

 uplifted above the sea-level, producing, by the Thanet Sands. The apparently 

 in the south-east of England, a gently perdurable flints, hurried downhill by 



