30 
POPULAE SCIENCE EEVIEW. 
determining the boundaries of the rock or rocks of which it 
is composed, and of drawing his lines to join with others in the 
surrounding area, would probably be safe enough, and some- 
thing more than mere conjecture. Moreover, with experience 
one notices many little facts that afford valuable hints in map- 
ping, which by a person not accustomed to the work would 
pass unnoticed : such as a slight feature in the ground, a 
spring, or some peculiarity of the soil. 
In mapping a country, therefore, the first thing is to get 
acquainted with the best sections ; to observe whether the rocks 
be of the stratified or unstratified kind, or both ; to observe 
their relations one to another, and also to the form of the 
ground. In sections of the stratified rocks we must examine 
each bed, and particularly notice the junction between any two 
formations, which if conformable may require some assistance 
from a study of the fossils to fix. We must carefully note any 
features such junctions may make in the ground, whether in 
the form of a terrace due to the resistance of some hard bed to 
denuding agents, or in the wetness or dryness of the soil, due 
to springs and the pervious or impervious nature of the rocks. 
We must also endeavour to ascertain to what extent the 
country is covered with drift deposits, and how far the soils 
may be an indication of the rocks beneath. The best sections 
are seen in a railway-cutting, a sea-cliff, a quarry, a deep road- 
cutting, or a foundation-pit. The sections recorded in a note- 
book are useful for comparison with other sections, so that 
some notion of the general character and thickness of each 
formation, and of the beds at different horizons in it, may be 
arrived at. Then, when one has a general notion of the rocks 
and their relations to one another, the boundaries between 
them may be traced out on the ground. The character of the 
mapping here, however, depends very largely upon the nature 
of the rocks ; if they be the older rocks, much disturbed and 
contorted, or penetrated by igneous dykes, or if they be secon- 
dary rocks maintaining great parallelism and conformity, or 
tertiary rocks covered irregularly by drift deposits. Having 
fixed all the clear junctions that may be observed in a pre- 
liminary survey of the best sections, one may then draw the 
lines which mark the junctions across the intermediate ground, 
noticing every section on the way, in the banks of a stream, or 
in ditches, which usually afford some indications of the strata. 
In the igneous and older stratified rocks one usually gets 
some bosses of the rock projecting here and there on the hill- 
sides, and even on the high roads. Attention must be paid to 
the general direction or dip of the older stratified rocks, great 
care being taken to discriminate between this and the “ slaty 
cleavage ” which cuts up the beds at all angles, and is a pheno- 
