68 THE JOURNAL OF GEOLOGY. 



the generalizations by wiiich they are correlated. The more 

 complete the mental scheme by which an ideal system of topog- 

 raphy forms is rationally explained, the more clearly can the 

 physical eye perceive the actual features of the land surface ; the 

 more definitely can it record them in mental impressions. Topo- 

 graphical forms are so varied, and often so complicated, that the 

 outer eye alone is no more competent to detect all their intrica- 

 cies and correlations than to discover all the peculiarities of the 

 tidal curves. It is true that with exceptionally keen powers of 

 observation, and with unusual opportunity for deliberate exami- 

 nation, the unaided eye may come to see more and more of the 

 ultimate facts ; but these conditions are so rare that they need 

 not be considered. The average eye, and the usual time allowed 

 for observation do not suffice ; they must be supplemented by 

 the quickened insight that comes from rational understanding. 



No better confirmation of this conclusion can be found than 

 in the experience of those who have to employ engineers, 

 untrained in geology and geography, to make topographical 

 maps. The work that such surveyors produce is rigid, mechan- 

 ical, unsympathetic, inaccurate, inexpressive. If time were 

 allowed them to run out all their contours by actual measure- 

 ment, an exact map might be produced ; but neither time nor 

 money can be devoted to so slow and expensive a method. Even 

 the best surveys are necessarily sketched in great part ; and the 

 topographer must appreciate his subject before he can sketch it. 

 He must have a clear insight into its expression ; his outer eye 

 must be supplemented by his inner eye. Then he can make up 

 a valuable, even though not an expensive, map. I do not mean 

 for a moment that he is to invent and not to observe ; that he is 

 to make a fancy picture instead of a true likeness. My point is 

 simply that the difficulty of making a true likeness is so great 

 that all aids towards it must be employed ; and one of the chief 

 aids to sharp outsight is clear insight. How can a clear geo- 

 graphical insight be gained ? 



An analogy with the study of the tides may still serve us. 

 The facts of the tides are first presented in what seems like a 



