Notices of Memoirs — The Geological Survey. 313 



been brought to the perfection that has since been attained. The 

 possession of a correct topographical map is absolutely necessary 

 as the groundwork of a detailed and accurate geological survey. 

 From the outset the Ordnance maps have afforded the topographical 

 groundwork on which all the geological surveying has been carried 

 on. For many years only the sheets of the general map on the one- 

 inch scale were available, but when, in the progress of the Ordnance 

 Survey, maps on larger scales were prepared, these, as already 

 remarked, were employed for geological purposes. 



All the mapping of the Geological Survey is now conducted upon 

 the Ordnance maps on the scale of six inches to one mile (xcri 6-0)5 

 as has been above remarked. 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 six northern counties 

 that they could be adopted. In Ireland, however, and in Scotland, 

 where they were obtainable from the commencement of the geological 

 operations, the whole of the work has been conducted upon them. 



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. Not only 

 is it then much easier to fix the position of geological boundaries, 

 but an amount of detail may be inserted for which, though of great 

 importance, no room can be found on the one-inch scale. The large 

 map serves at once as a map and a notebook, and numerous detailed 

 observations can be taken and recorded upon it at the localities at 

 which they are made. 



Occasionally, where the geological structure becomes excessively 

 complicated, and requires to be mapped out in much detail, maps on 

 the scale of 25 inches to a mile (2 sVu) are made use of. Ultimatel}', 

 however, all the work is reduced to the one-inch scale, this being the 

 scale on which the general geological map of the United Kingdom is 

 published. 



Geologists had made considerable progress in the study of the 

 solid rocks before much attention was paid to the looser superficial 

 deposits. The Geological Survey in this respect followed the general 

 rule, and for many years made no systematic attempt to represent 

 the numerous and often complex accumulations of superficial 

 materials. Some of these, indeed, were shown on the maps, such as 

 tracts of blown sand and river-alluvium. But it must be remembered 

 that in the south-western counties, where the Geological Survey 

 began its work, superficial deposits are of such trifling extent and 

 importance that they were not unnaturally ignored. Only after 

 most of the southern half of England had been completed was it 

 determined to map the surface-deposits with as much care and detail 

 as had been expended on the older formations lying beneath them. 

 It had been discovered that this course was necessary both on 

 scientific and practical grounds. In the first place, these superficial 

 accumulations contained the records of the later geological vicissitudes 

 of Britain, and were beginning to reveal a story of the protbundest 

 interest, inasmuch as it dovetailed with the history of the human 



