Soil 433 



HOAV ROCK BECOMES SOIL. 



The ^'hardheads" at Hope Farm, presumably break down eventu- 

 ally to supply potash and other elements to the plants living near the 

 dying rocks. Those of us who have been reared on the glacial drift 

 know that stony farms are fertile, though not always popular. Where 

 one can observe plants growing on rock-bottom it is learned that soil is 

 being formed — trees are the vigorous sappers and miners of the plant 

 kingdom. Their roots push along rock fissures, and by their insistent 

 growing, make the opening yet wider. Where trees were growing close 

 to the edge of a little precipice made by a joint plane in the shale rock 

 at Ithaca, N". Y., roots were observed along the seams, having apparently 

 come through six feet of solid rock from the trees of which they are a 

 part. 



It is plain that these trees get roothold below the surface soil, and 

 it is likely that they draw food and moisture from the rock, which is for 

 them a substantial hardpan subsoil. In moist climates a very thin layer 

 of detritus is sufiicient to serve as soil. I have noticed a little patch of 

 moss and grasses growing upon the flat outcropping of the shale. Upon 

 stripping it up — it made resistance — it was seen to be a felted turf an 

 inch in thickness. The under surface was white with fine roots, blind 

 fingers groping for crannies in the rock and finding every one. The 

 place on the rock was seen to be a little depressed and quite damp. Per- 

 haps the depression gave the first-comers their chance, but the colony in 

 possession had widened and deepened the place, for several fragments 

 of the shale were found to have been fetched away, when the turf was 

 lifted. The roots had pried these off with the help of frost, heat and 

 moisture, then grown around them. Even this thin soil is growing; the 

 old adage is reversed. The moss gathers the rock. — Howard B. Cannon. 



H— 28 



