4 o6 SCIENCE PROGRESS 



the water-level in the chalk down to the impermeable ground 

 beneath without ever having recourse to pumps. This is an 

 ample vindication of those who maintain that the passage of the 

 water-level in the chalk presents, as a rule, no serious difficulty, 

 and the experience has been since repeated at both the other 

 collieries. 



The pit has since been carried to a depth of about 700 ft., 

 well down into the zone of Ammonites varians, and has shown 

 all the prominent features that are recorded on the coast section. 

 The thickness of the Middle Chalk is 239 ft., compared with 

 231 ft. as measured on the coast. The slight apparent discre- 

 pancy may be accounted for by the fact that the coast measure- 

 ments are taken perpendicular to the dip, while the pit is, of 

 course, truly vertical. 



The trial pit at Tilmanstone, about a mile and a half to the 

 north of the Waldershare boring, was commenced in August 

 1906 with a diameter of 7 ft. It is situated on the outcrop of 

 the Uintacrinus-band, about 30 ft. above its base. When the 

 depth of 270 ft. was attained, the discovery of the thick seams 

 at Waldershare removed the speculative element, the pit was 

 widened to 14 ft., and operations thus recommenced in October. 

 Water was met at a depth of about 160 ft., but the passage of 

 the water-bearing chalk was accomplished without difficulty — 

 the total feed scarcely exceeding 5,000 gallons per hour : once 

 more a convincing reply to those who fear sinking through 

 chalk. 



The pit was rapidly sunk down to the base of the Gault, 

 and finally the Lower Greensands were struck at a depth of a 

 little over 900 ft. These of course are water-bearing ; * but the 

 conditions being novel, it was impossible to make all prepara- 

 tions in advance. The consequent delay should have been 

 about two months ; the manufacturers dragged this out into six 

 months, and during this long wait no yardage was accomplished 

 in the pit, though material progress was effected in numerous 

 ways that were indispensable to the works. Long headings 

 were driven in the hard chalk in the Grit Bed, the indurated 

 base of the zone of Rhynchonella cuvieri, and in the waterproof 

 chalk of Holastcr subglobosus immediately beneath. 



At length, by midsummer, the pumping installation was 



1 The quantity of water in the Greensand in this pit has since been shown to 

 be inconsiderable. 



