An important practical lesson on this subject is taught us by the study of the wise provisions of Nature. Not only does the milk of the mother contain all the elements of a nutritive food mixed up together—as the egg does also for the unhatched bird—but in rich natural pastures the same mixture uniformly occurs. Hence, in cropping the mixed herbage, the animal introduces into its stomach portions of various plants—some abounding more in starch or sugar, some more in gluten or albumen, some naturally richer in saline, others in earthy constituents; and out of these varied materials the digestive organs select a due proportion of each, and reject the rest. Wherever a pasture becomes usurped by one or two grasses—either animals cease to thrive upon it, or they must crop a much larger quantity of food to supply the natural waste of _all_ the parts of their bodies. It may indeed be assumed as almost a general principle, that whenever animals are fed on one kind of vegetable only, there is a waste of one or other of the necessary elements of animal food, and that the great lesson on this subject taught us by nature is, that, by a judicious admixture, not only is food economised, but the labour imposed upon the digestive organs is also materially diminished. SECTION VIII.—CONCLUDING OBSERVATIONS. In this little work, now brought to a close, I have presented the reader with a slight, and I hope plain and familiar, sketch of the various topics connected with practical agriculture, on which the sciences of chemistry and geology are fitted to throw the greatest light.