APPENDIX. 469 



guide : yet while nothing must be sacrificed to pre- 

 cision, a cultivated taste will contrive to produce a 

 pleasing effect through the harmony of colouring. But 

 the utility of such a map is much increased by thus 

 pointing out the affinities of rocks ; so that a glance 

 will teach more than long descriptions : while it is the 

 reproach of geologists to have hitherto neglected this. 

 On this subject, however, a few hints must suffice, 

 where details would be tedious. Thus, in a secondary 

 series, might the beds of limestone and of sandstone 

 be associated by congenerous tints, thus might primary 

 be distinguished from secondary strata, and thus might 

 the unstratified rocks be associated, and also contrasted 

 with the strata; with much more that I need not now 

 point out. 



If the dips of strata have been indicated by 

 strengthening the tint on the elevated edge, this 

 produces confusion : and though a dart with a num- 

 ber are preferable, we cannot convey a true idea of 

 dips and superpositions, without sections ; the data 

 for which can sometimes be procured, but must often 

 be inferred ; while imaginary must therefore be sub- 

 stituted for true ones, taking care to avoid hypothesis. 

 And by colouring these conformably to the map, with 

 a symbol declaring the line of the section, the geolo- 

 gist will have done all in his power to render his lar- 

 hours useful. 



III. On conducting and describing Geological 

 Observations. 



Though the surface is extensively covered with loose 

 materials, the rocks are sometimes exposed, as they 

 can often be discovered through artificial works. And 

 that which cannot be seen, is inferred through the 

 powers of geological analysis; whence we learn to ana- 



