130 L. E. HICKS — SOME ELEMENTS OF LAND SCULPTURE. 



be the primitive conditions of hardness in structural blocks, the tendency 

 of weathering is to soften them from the top downward, or, in other 

 words, to produce that set of conditions last supposed; hence the 

 weather curve should be convex upward.* 



Water Carres: horizontal and vertical. — The streams formed by the 

 rains falling upon continental blocks have still greater sculpturing power 

 than the weather. The rough edges are first scored down with ravines, 

 as a carpenter hacks timber with an axe before he dresses it with finer 

 tools. Some of the ravines lengthen into rivers and cut far back into the 

 land. Except raw and fresh ravines, which may be tolerably straight, 

 the path of flowing water is meandering. Graceful serpentine curves 

 mark the flow-line, curves which constitute the most charming elements 

 of scenery. These horizontal water curves address themselves to the eye 

 in the most clear and agreeable manner ; but there is another kind of 

 water curve, the vertical, not always visible to the bodily eye, but none 

 the less clear and real to the eye of the mind. If we follow up a short 



Figure 2. — Water Curve of Erosion. 



ravine cut in homogeneous material we shall find a gentle slope at first. 

 which gradually increases in steepness up to the crest of the escarpment. 

 The positions of successive points of the channel, with their true rela- 

 tive distances above base-level, if drawn to scale, would form a curve like 

 figure 2. This is the typical water curve of erosion. 



Concavity of water Curve. — The water curve is precisely opposite to the 

 weather curve, in that it is concave upward. In a short ravine it may 

 be plainly seen, but the vertical curve of a river is so much flattened and 

 extended that it can only be comprehended by the mind, not perceived 

 by the eye. Indeed, there is a sense in which this vertical water curve, 

 as defined by Gilbert, La Noe and Margarie and others, is not only im- 

 perceptible but purely ideal. It is seldom realized as a smooth curve. 

 uniformly increasing its gradient upstream, except for short streams 

 whose channels are cut in a homogeneous rock. The intervention of a 

 harder stratum makes a jog in the curve. All cataracts and rapids with 



♦ Compare La Noe and Margarie, " Formes du TerraiD," p. 26, pi. vii, fig. 15. 



