GEOLOGY. 
71 
making a journey through a tract of the earth’s surface, the geology of 
which is unknown, what will he the best method of procedure and the 
principal points to which he should direct his attention ? 
On the whole, the most useful record of a journey, whether intended 
for publication or merely as a memorandum, is a sketch geological map of 
the route followed, with the dips and strikes of the rocks and approxi¬ 
mate boundaries to the formations, supplemented by notes and sketch- 
sections. Where, as is commonly the case in mountain-chains, and fre¬ 
quently in less elevated portions of the country, the rocks are much 
disturbed, and especially if the number of systems exposed is large and 
the changes frequent, no traveller can expect to do more than gain a very 
rough and general idea of the succession of beds in detail, and of the 
structure; but by making excursions in various directions, whenever a 
halt is practicable, by searching for fossils as a guide to the age and for 
the identification of beds with each other, and by carefully noting the 
general dip and strike of the more conspicuous beds, it is often possible, 
especially if an opportunity occurs of retracing the road followed, or of 
traversing a parallel route, to make out the structure of a country that 
at first appears hopelessly intricate. Dense forest is perhaps the worst 
obstacle to geological exploration; snow is another, though not quite so 
serious a disadvantage. It is always a good plan to climb commanding 
peaks; the general direction of beds, obscure from the lower ground, not 
unfrequently becomes much clearer when they are seen from above. 
In level and undulating regions, on the other hand, it frequently 
happens that enormous tracts of country are occupied by the same 
formation, and if the rocks are soft, and especially if they are horizontal, 
or nearly so, little, if any, rock is to be seen in place. In this case 
water-courses should be searched for sections, and the pebbles found in 
the stream-beds examined, care being taken not to mistake transported 
pebbles derived from overlying alluvium or drift for fragments of the 
underlying rock. Where the same formation prevails over large tracts, 
it is usually easy, by examining the stones brought down by a stream, to 
learn whether any other beds occur. It is astonishing how even a small 
outcrop of hard rock at a remote spot in the area drained by a stream 
will almost always yield a few fragments that can be detected by walking 
two or three hundred yards up the stream-bed and carefully examining 
the pebbles. 
