Read it through once

So far it has been _subsoil_ and _underlying rock_, but now the roots begin to disintegrate and work up the subsoil; the earthworm has his chance, and forms true _soil_. On this particular hillside, the water would drain away and there would be no danger of mosses strangling and choking the Blaeberry and the Heather. The worm flourished and multiplied, and the soil became rich and black. Here and there a Sloe or a Rowan, or Poplar, or perhaps Alder and Birch, began to appear. In certain places Whins and Brooms, Brambles and Briers, diversified the hillside. Then a few Scotch firs began to push their way up, through the thickets. At first they were very small and stunted, but as each one formed a dense, deep-going mass of hardy roots, they were able to investigate the riches of the subsoil. Every year the amount of leaf-mould above increased, until the original moss-covering was utterly destroyed and a pine forest (see Chap. XXVIII.) occupied Pennell Brae.