144 The Work of the Geological Survey. 
equal in value, and frequently imperfect or even inaccurate in their 
topography. But since the Ordnance Survey was plotted on a large 
scale the accuracy attained has been so great and so invariable as 
to fill my colleagues and myself with admiration. It is on these 
most excellent maps that our geological lines are traced upon the 
ground, and on which they are ultimately engraved and published. 
So that although the old outward bond of connexion between the 
two Surveys has long been severed, the relationship between them 
remains as intimate and cordial as it has ever been. 
All the mapping of the Geological Survey is now conducted upon 
the Ordnance maps on the scale of 6 inches to 1 mile ( ro l 6 TT ). These 
maps were not available in England and Wales until about two- 
thirds of the country had been surveyed geologically, and it was 
only in the northern counties that they could be adopted. In 
Ireland, however, and in Scotland, they were obtainable from the 
commencement of the geological operations, so that the whole of the 
work has been conducted with them as a basis. It is impossible to 
overestimate the gain, both in completeness and accuracy, from the 
substitution of a large-scale map in the general investigation of a 
complicated geological region. For example, no more admirable 
piece of geological mapping had ever been achieved when the 
Geological Survey maps of North Wales, by Ramsay and his col- 
leagues, were published. That difficult region was surveyed on the 
1-inch scale, and excellent though the work still is, it is far inferior 
to what the same band of intrepid mountaineers could have ac- 
complished had they had the good fortune to be furnished with 
6-inch maps. Occasionally, when the structure becomes excessively 
complicated and when its details require to be mapped out clearly 
to be intelligible, maps on the scale of 25 inches to a mile are 
made use of. Ultimately, however, all the work is reduced to the 
1-inch scale, this being the scale on which the general geological 
map of the United Kingdom is published. 
Let me say a few words about the actual methods of geological 
surveying. The question is often asked of us, Do we bore or dig 1 
and when we answer in the negative, an incredulous smile may 
often be seen on the face of the inquirer, who evidently at once 
begins to doubt the trustworthiness of any surmises we may make 
as to what lies concealed beneath the surface. In reality, however, 
a trained geologist can generally tell, with a close approximation to 
accuracy, the character and arrangement of the rocks underneath 
his feet. There are many indications to guide him which do not 
strike the eye of the ordinary observer. So far from being guess- 
work, his conclusions are often based upon such an array of observed 
facts as to be irresistible. The first experience of a recruit who 
joins the service is to be trained in the practice of searching for 
geological evidence. He soon learns how unobservantly he had 
walked about before, and in how many ways he may detect indica- 
tions as to the direction of geological boundaries, even when the 
rocks themselves may generally lie out of sight. He finds that 
moles and rabbits help him greatly, by throwing up the subsoil for 
