Prof. Chapman's Mineralogical Notes. 119 



(4.) Chalk from the neighbourhood of Bletchingly in Surrey : 

 spec. grav. =2*49. Water absorbed by 100 parts = 15-60. 



(5.) Chalk from Tring : spec. grav. =2*482. Water absorbed 

 by 100 parts =15-12. 



(6.) Chalk from Luton in Bedfordshire : spec. grav. =2*477. 

 Water absorbed by 100 parts =1494. 



The mean of these results gives 16*83 for the amount of water 

 absorbed by 100 parts of chalk, corresponding to rather more 

 than 2\ gallons per cubic foot, or to very nearly 215 millions of 

 gallons per square mile of one yard in thickness. The absorbent 

 power, on the whole, may be greater in the upper chalk beds 

 than in those of the middle chalk ; but it should be observed, 

 that hard layers of comparatively low absorbent power occur 

 indifferently both in the upper and in the middle chalk, and, 

 indeed, in the lower division also ; for here, as in all other cases, 

 the mineralogical quality of the rock is entirely a local pheno- 

 menon. 



In addition to the above, specimens of chalk and chalk marl 

 from several other localities were likewise tested, but they fell to 

 pieces during saturation. One of the latter kind from the vicinity 

 of Eastbourne in Sussex was of so absorbent a nature, that a 

 specimen weighing 486*3 grs., and consequently of the bulk of 

 rather more than three-fourths of a cubic inch, crumbled into 

 powder, with a loud hissing noise, in less than ten minutes. 

 Under the microscope, the powder exhibited a multitude of Fora- 

 minifera belonging to the genera Lituola, Textularia and Cuneo- 

 lina, unless the forms which I attributed to the latter genus were 

 those of a very cuneiform species of Textularia. I could not 

 clearly make out the openings. 



Large masses and even layers of considerable extent of a hard 

 clunch-like substance called " pan w by the well-borers, from the 

 fact that it usually lines the water-channels in the chalk, occur 

 in many localities. A specimen from Hertfordshire which I 

 examined, and which was taken from a depth of more than 100 

 feet from the surface, consisted of a subcrystalline and more or 

 less siliceous limestone. H.=3*0 to 3*5; spec. grav. =2*54. 

 Amount of water absorbed by 100 parts =3*45. Insoluble 

 silicate of alumina was present to the amount of 8*28 per cent., 

 the remaining portion consisted of carbonate of lime with traces 

 of the carbonates of manganese, iron and magnesia. 



In some borings near Brighton these layers of " pan " were 

 not met with ; but the curious fact was brought to light of the 

 existence of a bed of brown clay, 16 inches thick, at a depth, 

 of 150 feet from the surface. A second clay bed of a blue colour 

 8 inches thick, was passed through at a further depth of 34 

 feet (or 184 feet from the surface), the boring still continuing 

 in the chalk. 



