55 



the chalk, but the china clay and the sand is believed to have been 

 derived from the disintegration of granite. The ancient Solent 

 river drained a vast extent of granite country to the west, of which 

 Dartmoor, Cornwall, and the Scilly Islands are all that now remain. 

 As the granite decomposed, its felspar formed fine white mud, 

 which has been left in beds of china clay, whilst the quartz dis- 

 integrated into sand of various degrees of fineness. Thus has the 

 scenery we now enjoy in our cliffs, the Purbeck Hills, and the 

 beautiful bays and harbours of South Hampshire, Dorset, and the 

 Isle of Wight, been gradually built up and carved out by the same 

 forces of Nature now working around us. 



On March 29th, Dr. Ord discussed Mr. Spicer's 

 Chalk Scenery lecture on Chalk Scenery. This meeting was 



of special interest, because the views held by the learned lecturer 

 on this subject were explained as being in advance of those usually 

 accepted by geologists, though they are gaining ground, and in his 

 (Dr. Ord's) opinion were undoubtedly the correct ones. This arose 

 from the fact that the type of scenery peculiar to chalk is quite 

 different from that produced by other formations, its nearest 

 analogue being that of limestone districts. There are splendid 

 examples of chalk scenery in the Isle of Wight, Purbeck Hills, and 

 the Wiltshire Downs. The chief characteristics are: (i) greatly 

 rounded hill contours ; (2) the valleys are sudden, steep, begin 

 abruptly, and are mostly dry, and tend to turn suddenly, sometimes 

 at right angles ; (3) " cirques " or " arm-chairs" head many valleys ; 

 (4) swallow holes are found in them, sudden copious springs show 

 extensive underground drainage, although the valleys themselves 

 are dry. These features are very different from the wide, open 

 valleys found in clays, sands and gravel, with their bottom streams 

 gracefully curving and meandering, with gently sloping origins and 

 surface drainage, and also from the steep gullies and torrents of 

 mountainous districts amidst hard, insoluble rocks. The explana- 

 tion of this difference is found in two factors: (1) the solubility of 

 chalk in rain water containing carbonic acid in solution, and (2) 

 the porous nature of chalk, enabling it to hold water in its pores like 

 a sponge. In these respects there is a close resemblance between 

 the behaviour of chalk and limestone, except that the latter is not 

 porous, but both tend to allow water to flow and escape by fissures 

 and joint planes ; whilst the issuing of streams from the chalk at 

 similar levels is due to the lower portions being saturated with 

 water and unable to hold the further supplies that soak through to 

 them from above, It is to the solubility of chalk in rain water that 

 the rounded contour of chalk hills and the "cirque" or "arm- 

 chair " shape of its valley heads is due. 



The concluding class of the series was held on 

 coast scessery. Wednesday> Apr ii I2thj on Coast Scenery. There 



are three factors in the formation of coast scenery : (1) the material 

 • — as regards hardness or softness, etc. ; (2) the way the rocks 



