These two mountain chains—the Mounth and Drumalban, the one running east and west, the other south and north, and intersecting each other—thus divided the country north of the Firths of Forth and Clyde into four great districts, two extending along the east coast, and two along the west, while each of the two eastern and western divisions were separated from each other by the Mounth. The two eastern divisions are watered by the two great rivers of the Tay and the Spey and their tributaries, the one flowing south and the other north from these mountain chains. The two western divisions are intersected by those arms of the sea or lochs, which form so peculiar a feature in the West Highlands. [Sidenote: The Grampians.] The lesser mountain ridges which proceed on either side of the Mounth, and separate the various streams which flow into the two great rivers from each other, terminate as the waters enter the plains of the Lowlands, and present the appearance of a great barrier stretching obliquely across each of the two eastern districts and separating the mountain region from the plain; but, although this great barrier has an appearance as if it were a continuous mountain range, and is usually so considered, it is not so in reality, but is formed by the termination of these numerous lesser ridges, and is intersected by the great rivers and their tributaries. This great barrier forms what was subsequently termed the Highland line, and that part of it which extends across the south-eastern district from Loch Lomond to the eastern termination of the Mounth was known under the general but loosely applied name of the Grampians.[6] Within is a wild and mountainous region full of the most picturesque beauty which the ever-varied combination of mountain, rock, and stream can afford, but adapted only for pasture and hunting, and for the occupation of a people still in the early stage of pastoral and warlike life; while every stream which forces its way from its recesses through this terminating range forms a pass into the interior capable of being easily defended. Throughout the early history of Scotland these great mountain chains and rivers have always formed important landmarks of the country. If the Mounth is now known as the range of hills which separate the more southern counties of Kincardine, Forfar, and Perth from those of Aberdeen and Inverness on the north, it was not less known to the Venerable Bede, in the eighth century, as the steep and rugged mountains which separate the provinces of the southern from those of the northern Picts.[7] If Drumalban now separates the county of Argyll from that of Perth, it formed equally in the eleventh century the mountain range which separated Arregaithel from Scotia,[8] and at an earlier period the boundary between the Picts and the Scots of Dalriada.[9]