48 OUTLINES OF FIELD-GEOLOGY KT i 



of the Scottish Geological Survey had to walk alxnit 

 2000 or 2500 miles in the course of the year. Every 

 square mile of his completed map re: . therefore, 



on the average, about twenty or twenty-five miles of 

 actual walking. It is useful to measure the length of 

 boundary-lines traced in each square mile surveyed, as 

 we thus obtain a kind of measure of the intricacy of the 

 work. In comparatively simple ground the ratio be- 

 tween area mapped and boundary - lines drawn 

 average about i to 3 or 4 ; that is to say, every square 

 mile surveyed involves the tracing of three or four miles 

 of boundary. In the Highlands the annual average 

 of square miles surveyed is considerably less, but the 

 intricacy of the geological detail and the physical diffi- 

 culties presented by the ground are incredibly gr 

 The climate, too, presents serious drawbacks in its wet- 

 ness and storms; and the working season is much 

 shorter than in more genial parts of the country. So 

 complicated is the geological structure in some parts of 

 the Highlands that the ratio between area and boundaries 

 rises to as much as i to 1 7 or more, each square mile 

 examined requiring 1 7 or more miles of boundary to be 

 traced. 



It will be readily believed, that with all the advant- 

 ages for field-geology in Britain it should be possible 

 here to construct the most elaborate geological maps. I 

 would refer to some of the published sheets of the Geo- 

 logical Survey of the United Kingdom for an illustration 

 of what can be, and has been, done in this respect I 

 do not suppose that any such detailed geological work 

 has been elsewhere attempted. The large maps on the 



