I 



ON THE DIP OF THE UNDERGROUND PALEOZOIC ROCKS. 447 



apparatus must be connected were t)f steel, and would in all probability 

 so disturb the movements of the magnet as to lead to erroneous conclu- 

 sions. So also, masses of iron in the earth might cause deflection, whilst 

 there would be nothing to indicate that such had occurred. The idea of 

 attempting to trace the magnetic meridian on the rock was consequently 

 abandoned, and it was next considered how the core, or a cast of it, could 

 be marked with some other known line of direction. To do this, the 

 carrier of the marking apparatus, or of the plastic material, must be 

 placed over the centre of the hole, with a horizontal line, the bearing of 

 which is known, marked upon it. It must then be lowered to the bottom 

 and made to operate without receiving the slightest permanent twist 

 during any part of the movement. This maintenance of a marked 

 diameter always in the same azimuth was the most difficult requirement 

 to fulfil. The earliest proposal was, to stretch a pair of fine steel wires verti- 

 cally between a core tube (fig. 6), used as a marking frame, and the top of 

 the boring stage, at .30 feet above ground. These wires were to be on 

 opposite sides of the axis of the boring-rods and at equal distances there- 

 from, but no nearer to each other than was necessary for clearing the 

 sides of the bore-pipe all the way up. They were to be made fast at their 

 lower ends to the core tube, but at the top were to be passed over pulleys, 

 and attached to heavy counterbalance weights for keeping the lines tightly 

 strained during the descent of the marker. There would thus be about 

 30 feet in height of each always visible, and by placing a theodolite on 

 one side, in the plane of the wires, one of them could be kept under 

 observation, and any deviation from the vertical that might be caused by 

 unavoidable rotation seen, whereupon the marker would be at once 

 restored to its correct position by moving the rods round at top. But the 

 length of wire exposed would have been so small, compared with the full 

 depth of the hole, that it was feared a considerable amount of twist might 

 occur at bottom without detection by the instrument. That plan was 

 consequently given up, and means were contrived for observing the boring 

 rods themselves, and guiding them in such a manner as to prevent all 

 possibility of twist. The details of this arrangement I will now explain. 

 On the circumference of the crown or tube carrying the marker, the 

 ends of a diameter were indicated by differently shaped notches. At the 

 commencement of an experiment, the tube was suspended with these 

 notches opposite to two sharp 



pointers (fig. 7), which were ^'^^- '*• 



firmly fixed at the Ifevel of the v^/222Z222>*- Ovtm' 



ground line on opposite sides /^^ ^\X 



of the hole, and at such a dis- f o\ f/ v\^ff(] \ 



taiice from its axis as just to '-^ lC/t\ n^~^^v\F~~^ "^ 



clear the crown. The pointers ^<K ^ y^ 



were hinged to fold back, so x^252zzzz^^'^''^^^'"'^ "^''^^ 



as to leave ample space for the Scale, i in. to 2 ft. 



core-tube to pass freely down. 



I should mention that the boring-rods at Ware were made of steel 

 and were tubular, 1^ inches inside and 2^ inches outside diameter, and 

 feet in length, with screwed ends (fig. 8). They were coupled up by in- 

 ternally screwed sockets, but when being lowered or raised they were 

 connected or disconnected in 30 feet lengths. At about 6 feet from the 

 axis of the hole, in a convenient direction, was hung a long fine plumb-line 

 (fig. 9), towards which a horizontal radial arm, clamped on the boring-i'ods 



