(.1 < NJOGIC M. MAPI 37 



the labour, \.\.- <lder geological formations on one 



copy of the map, the superficial accumulationt and soil* 



on another, the industrial information on a third, and so 



on. Hut without attempting to express all the detail 



possible, we may construct a correct and serviceable 



geological a distrit by generalising 



a, so as to give at a glance a broad and 



clear view of the distribution of the > and the 



i i K lints of geological structure. 



Geological S tain and Ireland is 



constructed chiefly upon field -maps (Ordnance Survey) 

 on the scale of M\ inches to the .te mile, or 



TV io f nature, but some limited districts, where great 

 detail is required, have been surveyed on the scale of 

 tweni lies to the mile. The information is pub- 



lished on the scale of one inch to , or g s J ao , and 



on a reduced general map of four miles to an inch, or 

 irArs- A convenient scale for a generalised map of a 

 country is ten miles to an inch or ss'oo- The smaller the 

 scale the less detail is possible, and the more care must be 

 taken to select geological features of prime consequence. 

 re important than the scale is the correctness of the 

 topographical map which is to serve as the basis of the 

 geological one. Unless the geography be accurately 

 icd, geological lines may be distorted, sometimes to 

 an extent whi h seriously interferes with the value of the 

 map. The importance of this point will be understood 

 from two diagrams (Fig. 3), which represent the influence 

 rect and incorrect topography upon geological lines, 

 It will be observed that the same district is represented 

 in both drawings ; the streams and their tributaries are 



