Notices of Memoirs — The Geological Survey. 315 



The survey of the superficial deposits thus combines a wealth 

 of geological interest with a great deal of practical value. The 

 geologist may find in it the solution of some problems and the 

 presentation of many more ; while the farmer, the watei'-engineer, 

 the builder, the road-maker, and the sanitary inspector may each 

 in turn gain practical information from it for his guidance. 



For purposes of distinction, the mapping of the formations of 

 every age that lie beneath the recent superficial deposits is known 

 in the Survey by the somewhat unhappily selected epithet of the 

 " solid geology." The object in this part of the field-work is to 

 represent on the maps the exact area which every formation or 

 group of rocks occupies at the surface, ot immediately below the 

 soil and drift, together with all, indications that can be obtained of 

 its structure, such as its variations of inclination, its changes of 

 lithological character, and the dislocations by which its outcrop 

 is affected. While the basis of the woi'k is rigorously geological, 

 facts having an industrial bearing, such as the presence of useful 

 minerals, or the depth and variations in thickness of water-bearing 

 strata, are observed and recorded. 



In those districts of the country where the rocks have long been 

 well known and where the geological structure is simple, the duties 

 of the surveyor are comparatively light, though it often happens 

 there that the simplicity of the " solid geology " is compensated for 

 by a great complexity in the overlying "drifts." Where, on the 

 other hand, the rocks are varied in character and complicated in 

 structure, where they are partially hidden under suioerficial deposits, 

 and where they rise into mountainous ground, difficult of access 

 and hard to traverse, geological surveying becomes a most laborious 

 occupation. In such a region as that of the North-West Highlands 

 of Scotland, for example, where the physical impediments are 

 gi'eat, where the ground is often both rugged and lofty, where 

 the climate is wetter and more boisterous than almost anywhere 

 else in Britain, and where the quarters to be had are often sorry 

 enough and remote from the scene of work, the surveyor has need 

 of all his enthusiasm to carry him bravely through these preliminary 

 obstacles. But when he comes to unravel the structure of the 

 rocks, he may find it to be sometimes almost incredibly complex. 

 He has to climb the same cliff, scour the same crag, and trudge 

 over the same moor again and again before he begins to perceive 

 any solution to the problems he has to solve. 



If the complicated " solid geology " of such a region is enough 

 to tax to the utmost the capacity and energy of the geologist, his 

 task is made still more difficult by the necessity of keeping his 

 eye at the same time ever open to all' the variations of the superficial 

 deposits, which in these rugged tracts are often singularly intricate, 

 though they may also be fascinatingly interesting. The ice-strife 

 on the rocks, the scratched stones high on the mountain-sides that 

 mark where the till once lay, the varieties of boulder-clay, the sand 

 and gravel eskers, the scattered erratic blocks and the detection of 

 their probable sources of origin, the moraine-mounds fringing or 



