The Victoria Cave, where the demarcation between the strata was very distinct, was explored, while the work was under my direction up to September 1873, in a somewhat similar fashion. It was, however, impossible on account of the great depth of the deposits to cut a passage down to the rock at the entrance. We therefore examined the superficial strata throughout the cave, merely gauging the thickness of those below by sinking three shafts. Where a cave is sufficiently high to allow of the work being carried on, it is better to clear out one stratum before another is disturbed. The most elaborate and perfect method of cave exploration is that which has been used by the committee in Kent’s Hole, under the superintendence of Mr. Pengelly, who writes as follows:[274]-- “The following is the method of exploration which has been observed from the commencement, and which it is believed affords a simple and correct method of determining the exact position of every object which has been found. “1. The black soil accessible between the masses of limestone on the surface was carefully examined and removed. “2. The limestone blocks occupying the surface of the deposits were blasted and otherwise broken up, and taken out of the cavern. “3. A line termed the ‘datum-line,’ is stretched horizontally from a fixed point at the entrance to another at the back of the chamber. “4. Lines, one foot apart, are drawn at right angles to the datum-line, and therefore parallel to one another, across the chamber so as to divide the surface of the deposit into belts termed ‘parallels.’ “5. In each parallel the black mould which the limestone masses had covered is first examined and removed, and then the stalagmite breccia, so as to lay bare the surface of the cave-earth. “6. Horizontal lines, a foot apart, are then drawn from side to side across the vertical face of the section so as to divide the parallel into four layers or ‘levels,’ each a foot deep. “Finally each level is divided into lengths called ‘yards,’ each three feet long, and measured right and left from the datum-line as an axis of abscissæ. “In fine, the cave-earth is excavated in vertical slices or parallels four feet high, one foot thick, and as long as the chamber is broad, where this breadth does not exceed thirty feet. Each parallel is taken out in levels one foot high, and in each level in horizontal prisms three feet long and a foot square in the section, so that each contains three cubic feet of material.