GEOLOGICAL SECTIONS. 41 



zero at the top, so that the instrument can be used 

 inverted, and placed to the under-side of a bed if 

 required. 



To take the dip of a bed in a pit, quarry, or elsewhere, 

 clear away the material from its upper surface in a part 

 as flat as can be found, and which follows as nearly as 

 the eye can detect the general line of the whole mass 

 exposed. Place the clinometer on this, or what is a 

 better plan, on a stick, or hammer-handle, first laid on the 

 rock ; this being of greater length than the instrument 

 is less liable to error from an undulating surface. See that 

 the clinometer is directed along the steepest part of the 

 cleared surface, which is probably not in a line with the 

 face of the pit also that the pendant is swinging freely 

 at the time ; when it comes to rest, read off the number of 

 degrees and make a note of the result. In some cases, 

 as beneath a ledge of rock, in a mine, or in a cavern, it 

 is more convenient to take the dip from the under-sur- 

 face of a bed, when, by the upper edge of an ordinary 

 clinometer, or by the inversion of the compass-form of 

 instrument, the same result may be obtained. In other 

 cases neither the upper- nor under-surface of a bed can 

 be got at without much labour, when the hammer- 

 handle or stick should be held along the exposed face, 

 as nearly as may be in the line of the bed, and the 

 clinometer placed thereon. Again, beds may be ex- 

 posed in cliffs or deep pits, at such a height or in such 

 a position as to be not readily accessible ; under these 

 circumstances, the observer should take his stand at a 

 good distance from the face of the cliff or quarry, at 

 right angles, or thereabouts, to the spot where he wishes 

 the dip to be determined. Holding the instrument 



