Page:Australia, from Port Macquarie to Moreton Bay.djvu/43

 and the temperature of the air is, of course, proportionate to its great elevation.

One remarkable characteristic of the round-topped ranges in the bases of the lower MacLeay, is their very great fertility: for their steep slopes are never bare and rocky, but almost invariably covered with soil, clothed with good grass and lofty forest trees, and sometimes tangled brush; they are occasionally stoney on the higher ridges, but the grass is still abundant. A peculiarity I have noticed in the soft, slaty ranges, is the very great inclination of the sides of ranges and gullies, having a good covering of soil, with grass and trees, and which I have seen considerably greater than that which geologists seem to have assigned as the extreme limit at which rock can carry a soil. I have extracted from Professor Jameson's valuable notes to Cuvier's Theory of the Earth, the following observations of the celebrated Humboldt on this subject. According to his measurements, "a slope of even fifteen degrees appears steep, and a declivity of thirty-seven degrees so abrupt, that if it be covered with a dense sward, it can scarcely be climbed. The inclination of the pastures of the Alps seldom exceeds an angle of ten or fifteen degrees, and a slope of twenty degrees is pretty steep. At an inclination of forty degrees the surface of the rock is sometimes covered with earth bearing a sward, but at a greater elevation the rocks are usually destitute of soil and vegetation. In the Upper Hartz, the most common