Webb John Seymour

“ The upper surface of a rock is that which presents itself most frequently, and the mode of observing it may be thus described.
As the surface of a rock afforded by a strata-seam seldom approaches to a perfect plane, a part of it must be chosen, which appears to give the mean, or average position of the stratification. if the surface be smooth, the quadrant may be fixed upon the plate, before the plate is set down upon the rock. If the surface be rough, the plate must first be set down, and adjusted by the eye, till its surface appears to coincide with the mean position of the stratification ”

“ No regard need be paid to the situation of the zeros of the plate.
The radial bar must be set home upon the base; and while one hand presses the plate firm against the rock, the other must be applied to the head of the screw g, and bring the quadrant round till the level, properly adjusted by turning it upon its axis, is horizontal. Its axis will now be parallel to the line of stretch, that is, to a line determined by the intersection of the plane of the stratification with the plane of the horizon. ”

“ CC is its base, which traverses upon the plate; at e is the button of the central axis, which is secured in the center of the plate by the hollowed end of the bolt beneath, and at f is the clamp and milled-head screw, for fixing the quadrant to the edge of the plate in any direction. At l is a rectangular aperture, through which the divisions of the plate are seen, and read off by an index on the middle of the bevelled side of the aperture nearest to the central axis. DD is the graduated arch, fixed firmly to the base, and at right angles to the plane of its under surface. ”