zoological and botanical province. It is curious and instructive to observe how well this statement accords with late geological discoveries. From a series of ascertained facts the student of physical science is enabled to speculate on a time when equatorial Africa was divided from the northern portion of the continent by a great sea, of which the Sahara formed the bed; it extended from the Gulf of Cabes to Senegambia in the west, and was many hundred miles in breadth. The Mediterranean sea did not then exist; therefore there was no great obstacle to the southern migrations of animals until they reached the shores of the great central African sea; but as there was no desert in those days, there would be no hot winds to temper the climates northward, and consequently we should expect to find traces of more rigorous winters in central and southern Europe; and such have been clearly proven by certain evidences, which were lucidly explained by Sir Charles Lyell at the last meeting of the British Association. Thus, although we may wonder at the extraordinary intelligence which prompts the bird to cross the Mediterranean, we see at the same time that it is going to no foreign land, where it will not meet friends to cheer it, or food unsuited to its wants. The two great causes which bring about the regular migrations of birds are either change of climate or failure of food--most often both combined. Any ordinary observer must have often remarked that the first effect of a decrease in temperature in autumn is the sudden disappearance of many winged and wingless insects, on which many soft-billed birds of passage depend. At that season swallows, that seemed so full of life and vigor, skimming over fields, threading along the lanes, or twittering from straw-built sheds, are soon seen collecting in flocks, and flitting about with a marked diminution in their activity--now huddling together on the eaves of houses, or assembling in long lines on the telegraph wires; another boreal blast, not yet sufficient to turn the leaf, sends the whole flock southward, for they soon find that there is no use facing the north from whence the cold puffs are coming, whilst by holding in the direction of the sun, with the balmy southern winds occasionally beckoning them to advance, they soon gain the object of their desires. Thus flocks may be seen pursuing their journey, and picking up a livelihood and more companions as they speed their way over mountain, moor, field, city, or sea to {59} the sunny climes and eternal sunshine of southern Europe and trans-Mediterranean lands. The majority of migratory birds cross the latter sea during the vernal and autumnal equinoxes; whilst a few, such as certain finches and water birds, make their appearance on the islands and southern shores throughout the winter; the latter, however, are in a great measure dependent on the state of the weather, and their numbers increase or decrease accordingly.