93 



the silica, alumina, and a portion of the water to form a mass of 

 interlacing, hydrated crystals. The cement sets long before the 

 formation of the crystals is complete, but the hardness increases 

 as more and more of them are formed. 



Calcium Phosphide is made by the direct action of phosphorus 

 upon heated lime. When treated with water a spontaneously in- 

 flammable gas, called phosphine, is produced. 



Calcium Phosphate contains oxygen as well as calcium and 

 phosphorus. It is an important constituent of bone and occurs 

 in apatite and other minerals. It is the source from which phos- 

 phorus itself is obtained. 



Within the limits of a single lecture only a brief account of 

 the chemistry of calcium can be given. My aim will have been 

 attained if this sketch should prove a useful introduction to the 

 other lectures of the series. 



(Read before the Geological Section, February 18th, 1915. 

 HALK is the limestone most generally known in the South 



V* of England, where several ranges of downs radiate eastward 

 and southward from Salisbury Plain and terminate on the coasts 

 in the magnificent white cliffs, which give our country one of its 

 earliest names. The chalk forms the rim and floor of two wide 

 basins, the London Basin and the Hampshire Basin, which 

 between them comprise the whole country lying to the south-east 

 of a line roughly drawn from the Wash to Bridport in Dorset, 

 excepting only where they are separated by the denuded Wealden 

 anticlinal arch and its small counterpart the Kingsclere arch ; com- 

 paratively small areas in the Isle of Wight and the " Isle of Pur- 

 beck," which lie to the south of the chalk scarps must also be ex- 

 cluded. In our own district the downs form most of the high land ; 

 Cranborne Chase links up the downs about Salisbury with the 

 Dorset Heights, which form the highlands of Mid-Dorset ; these 

 last turn eastward and continue as the narrow ridge of the back- 

 bone of Purbeck, and end at the coast in the cliffs of Handfast 

 Point, which look out across the Bay to the chalk of the Needles 

 and of the Isle of Wight much as the Culvers at the other end 

 of the Vectian chalk range look up Channel. 



The Chalk of England now lies wholly south of the escarp- 

 ment previously mentioned, except for the outliers in Devon and 

 the extensions to the north which form the Lincolnshire and York- 

 shire Wolds. There is little doubt, however, that chalk formerly 

 covered all England and Wales, with the possible exception of the 

 higher peaks of the west and north, as well as much of the low- 



II. 



The Geology of the Local Chalk. 



By W. Munn Eankin, M.Sc, B.Sc. 



