Page:The Journal of geology (IA journalofgeology21894univers).pdf/82
the generalizations by which they are correlated. The more complete the mental scheme by which an ideal system of topography 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. Topographical forms are so varied, and often so complicated, that the outer eye alone is no more competent to detect all their intricacies 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 examination, 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, mechanical, unsympathetic, inaccurate, inexpressive. If time were allowed them to run out all their contours by actual measurement, 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 geographical 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