GEOLOGY. 
67 
determined with a very short straight-edge. As a rule, except with very 
low angles of dip, the variation in the inclination of the rocks themselves 
exceeds the limits of error of the instrument. A little care, however, is 
necessary in taking dips ; for the apparent dip seen in a section, such as 
is often exposed in a cliff, may differ widely from the true dip, which will 
only be shown if the section runs at right angles to the strike of the 
beds. Dips seen on the sides of hills at a distance are but rarely correct 
for the same reason. 
A prismatic compass and an aneroid are frequently of great service: 
the former to determine the position on the map, if one exists, and to 
aid in making a rough map, if there is none ; and the latter to estimate 
roughly the heights on the road travelled, especially in mountainous 
countries, and also to measure the thickness of horizontal beds. Both 
form a part of the outfit of most modern travellers. A good aneroid 
gives sufficiently accurate determinations of height for a rough but 
adequate geological section across any country, if the distances are 
known. 
Collections .—Geological specimens require little more than paper and 
boxes for packing. Occasionally fossils or minerals are fragile, and need 
tow or grass to protect them from injury; but there is no risk from the 
animal and vegetable enemies of zoological or botanical collections. The 
only important point to be borne in mind is that every specimen should he 
labelled on the spot , or, at all events, in the course of the day on which it 
is collected. Strong paper is best for labels, and these should not be put 
up in contact with the rock-fragments themselves, or they will be worn 
by sharp edges and become illegible, if not rubbed to fragments. Always 
wrap each specimen in paper, or some substitute, then add the label, and 
then an outer covering. The label,* if nothing else is written, should 
always record the locality distinctly written. 
* Travellers in tropical countries will do wisely to poison all their labels before 
using them, to preserve them from attacks of insects and mites. Washing with 
a very weak solution of corrosive sublimate is an efficient plan. A large number 
of labels, with the collector’s name printed on them, may be taken, and if made 
of strong thin paper they will not occupy much space. Bank-note paper is well 
adapted for the purpose. Any writing should be, if possible, in ink; if not, a 
very hard black pencil should be used. 
F 2 
