ACCOUTREMENT OF A FIELD-GEOLOGIST. 711 



This is the instrument employed in the Geological Survey. It is car- 

 ried in a leather case, or pocket, hung from the waist-belt on the side 

 of the body, opposite to the hammer (Fig. 1). The directions of the 

 dip and strike of rocks, the trend of dislocations and dikes, the line 

 of boundaries, escarpments, and other geological features, are observed 

 accurately, and noted on the spot at the time of observation, either 

 on the map or in the note-book. A convenient instrument for light 

 and rapid surveys, or reconnaissances, combines the compass and the 

 next instrument I have to describe the clinometer. I shall refer to 

 it again. 



The clinometer, or dip-measurer, is employed to find the angle at 

 which strata are placed to the horizon an important observation in 

 the investigation of the geological structure of a country, and one 

 having frequently a special economic value as, for instance, when it 

 points out the depth to which a well or mine must be sunk. Various 

 patterns have been proposed and used for this instrument. Formerly 

 a spirit-level was commonly employed. But, apart from the difficulty 

 of rapid adjustment for the requirements of the field, the spirit-levels 

 in the clinometers were apt to get broken. A much more portable and 

 serviceable form of clinometer may be made by the geologist himself. 

 It consists of two thin leaves of wood, each two inches broad and six 

 inches long, neatly hinged together, so as to open out and form a foot- 

 rule when required (Fig. 2). On the inside of one of these leaves a small 

 brass pendulum is so fixed that when it swings freely and hangs verti- 

 cally it forms an angle of 90 with the upper edge of the leaf to which 



Fig. 2. The Clinometer. 



it is attached. An arc, graduated to 90 on each side of the vertical, 

 is drawn on the wood, or on paper or brass fastened to the wood, so 

 that when the leaf is moved on either side the exact number of de- 

 grees of inclination is shown by the pendulum on the graduated arc. 

 The corresponding face of the opposite leaf is hollowed out just 

 enough to let the two leaves fit closely, and keep the pendulum in its 

 place when the instrument is not in use. This form of clinometer, 

 made of boxwood and bound with brass, may be obtained of instru- 

 ment-makers. It is light and strong, and its durability may be under- 

 stood from the appearance of the instrument which I hold in my hand, 



