Felspar. Hornblende. Silica, 65 42 Alumina, 18 14 Potash and soda, 17 trace. Lime, trace. 12 Magnesia, ” 14 Oxide of iron, ” 14½ Oxide of manganese, ” ½ ----- ------- 100 97 [15] The reader is referred for more _precise_ information to the author’s “LECTURES,” pp. 377 to 390. Thus theory shews, that while granite soils may be eminently unfruitful, trap soils may be eminently fertile. And such is actually the result of observation and experience in every part of the globe. Unproductive granite soils cover nearly the whole of Scotland north of the Grampians, and large tracts of land in Devon and Cornwall, and on the east and west of Ireland; while fertile trap soils extend over thousands of square miles in the lowlands of Scotland, and in the north of Ireland; and where in Cornwall they occasionally mix with the granite soils, they are found to redeem them from their natural barrenness. While such is the general rule in regard to these two classes of soils, it happens on some spots that the presence of other minerals in the granites, or of hornblende or mica in larger quantity than usual, give rise to a granitic soil of average fertility, as is the case in the Scilly isles; while, in like manner, the trap rocks are sometimes, as in parts of the isle of Skye, so peculiar in constitution as to condemn the land to almost hopeless infertility. In some districts the decayed traps are dug up, and applied with advantage, as a top-dressing, to other kinds of land; and as by admixture with the decayed trap, the granitic soils are known to be improved in quality, so an admixture of decayed granite with many trap soils, were it readily accessible, might add to their fertility also. SECTION II.—OF THE SUPERFICIAL ACCUMULATIONS OF TRANSPORTED MATERIALS ON DIFFERENT PARTS OF THE EARTH’S SURFACE. It is necessary to guard the reader against disappointment, when he proceeds to examine the existing relation between the soils and the rocks on which they lie, or to infer the quality of the soil from the known nature of the rock in conformity with what has been above laid down,—by explaining another class of geological appearances which present themselves not only in our own country but in almost every other part of the globe.