234 Geological Survey of Great Britain. 
considerable danger. Yet Mr Ramsay submitted to it with 
untiring zeal, and left no spot till he had safely established 
the boundary line by frequent comparison and repeated ob- 
servation. 
The districts surveyed by the assistants and geologists, 
are, finally, revised every spring by the director, when faults 
on the part of beginners are corrected, and, if necessary, re- 
surveyed ; moreover, Sir H. De la Béche himself from time 
to time crosses the country, in arbitrarily-chosen directions, 
to satisfy himself personally of the correctness of the work. 
In this manner, a degree of exactness is introduced into the 
geological maps, which appears to be the utmost that can be 
attained on the scale selected for the purpose. 
Simultaneously with the determination of the boundary- 
lines of the rocks, observations on the strike and dip of the 
beds, and other remarkable phenomena, are made and entered 
in note-books. The fossil collectors are despatched to the 
localities where fossils are found to be most numerous, and 
the organic remains, one may say of each individual bed, are 
specially collected and sent to London. | 
After the completion of the geological map of a district, 
they proceed to the construction of sections, in all these di- 
rections which give promise of interesting results, and the 
work is conducted throughout with geometrical accuracy. 
The sea-level serves as the datum line in all; the form of 
the surface is measured with the theodolite and chain, the 
dip of the beds is taken with the clinometer, and in this man- 
ner they obtain a perfectly natural representation. 
Besides the geological sections, whenever it appears 
feasible and interesting, drawings are taken of the succession 
of beds in shafts, although, in most cases, these have not been 
measured by the members of the Survey, but were commu- 
nicated by the owners of mines. All these measurements, 
which, of course, are often taken in a line inclined to the 
plane of stratification, are reduced to a line at right angles 
to it, in order to represent at once the true thickness of the 
several rock-strata. 
e 
Z. 
