
276 STRUCTURAL AND FIELD GEOLOGY 
which with choice but weighty material is often too great 
to be resisted. 
Lhe Lens.—This is an important adjunct, and is so easily 
carried that no field-geologist should be without it. Even 
the best eyesight may fail to diagnose the finer grained rocks, 
but there are few of these the character of which cannot be 
determined by means ofa lens. For all ordinary purposes a 
lens with two powers will be sufficient. 
The Compass.—TVhis instrument is primarily used to 
determine the direction in which strata are inclined, and for 
this purpose any pocket compass will serve. It is often very 
desirable, however, to take bearings in order to fix the trend 
of some dyke, fault, or other structure, or to determine the 
exact position where some observation is made. This is 
readily done by means of a prismatic compass. An instrument 
of this kind, however, is seldom required by the student who 
is provided with an accurate large scale map, such as the 
6-inch map of the Ordnance Survey. 
The Clinometer.—W ith this instrument the angle of dip is 
measured in the manner already described (p. 127). 
The beginner will probably find it most convenient to use 
an instrument in which compass and clinometer are combined. 
Being the size of an ordinary watch it slips easily into the 
waistcoat pocket.* The chief drawback to this instrument is 
that the edge which is to be held parallel to the line of dip is 
too short. The edge may be “lengthened,” however, by 
placing it on the note-book, the hammer-handle, or the 
walking-stick—if the geologist feels it necessary to burden 
himself with one. He will find ere long that a stick is rather 
a hindrance than a help, and will probably succeed in losing 
it before his first day’s work is done. 
The Note-book.—This should not be too small nor yet too 
large to slip into a side-pocket. A convenient size is 6 inches 
by 4 inches—for the book when opened can then be used as 
a rough-and-ready foot-rule for measuring purposes. The 
paper may be plain or ruled according to taste. As the book 
is meant, however, to contain not only notes and descriptions 
but sketches of geological sections, it is advisable to have 
* A very serviceable instrument of this kind is supplied by Messrs 
Troughton & Simms, 138 Fleet Street, London. See Appendix E, 

