ox THE DIP OF THE UNDERGROUND PALAEOZOIC ROCKS. 449 



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side of the circle, thus nicarking distinctively the one end of the diameter from 

 tlie other. Crown and cutters were carefully lowered into the bore hole 

 and over the core at its bottom, with every precaution to maintain the 

 aforesaid diameter in the same known direction. They were then brought 

 up with the same care, and so successfully, that the crown returned to the 

 surface with its marked diameter exactly in the 

 direction in which it began to be lowered. 



As a check upon what had been done, a cast was 

 then taken of the rough top of the stone. To do this, 

 a tube of a size to encircle the core (fig. 11) was pre- 

 pared by fixing a diaphragm in it at a distance of 9 

 inches above its lower end, and filling in beneath this 

 diaphragm, to a depth of 6 inches, a mass of wax, 

 softened with spirit of turpentine, and coloured with 

 Venetian red. A diameter was marked, as in the 

 preceding case, by notches at either end, and the 

 whole was lowered upon the core with the same care 

 to keep the marked diameter in the proper azimuth. 

 Just before making the imprint, water was pumped 

 through a pipe, \\ inches in diameter, that passed 

 down the middle of both diaphragm and wax. There 

 was thus removed from the top the sediment that 

 would otherwise have prevented a true impression 

 being obtained. The weight of the core-tube, rods, 

 and boring head, was counterbalanced, so that a pres- 

 sure of only 10 lbs. per square inch came upon the 

 surface of the wax, but nevertheless, great difficulty 

 was experienced in arriving at the proper consistency 

 for the plastic material. If too soft, it would not 

 retain its place until it reached the bottom, and if 

 too hard, a satisfactory print could not be obtained. 

 After several failures, the right admixture was hit 

 upon, and a cast secured. The tube, with its mould 

 of wax, was then brought up, without having received 

 the slightest twist from the time it began to descend 

 to the time at which it again reached the surface. The 

 core-extractor was afterwards sent down to bring up 

 the marked core for examination. On its arrival at (^ 

 the surface, the three cutter marks were seen in the 

 form of vertical chases more than three feet each in 

 length on the outside of the cylinder of rock, and the 

 irregularities of the top face completely corresponded ir 

 with those appearing on the wax cast. By tracing V\ 

 on the upper end of the core, the diameter marked 

 on the wax carrier, it was found to coincide exactly ij 

 with a line passing through the single chase and mid- scale, i in. to 8 ft. 



way between the pair of chases, afi'ording a complete 

 proof of the accuracy with which the proper direction had been maintained 

 during lowering. 



The Committee being anxious to have full confirmation in every respect 



of the results thus obtained, a further test was devised. The bottom of 



the hole was faced up quite level by the revolution of suitable cutting 



edges, and a groove about 6 inches deep was formed around the circum- 



1895. G G 



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