Proceeding farther north, the great series of the mountain ranges, stretching from the south-west to the north-east, present one continuous barrier, intersected indeed by rivers forming narrow and easily defended passes, but exhibiting the appearance of a mighty wall, which separates a wild and mountainous region from the well-watered and fertile plains and straths on the south and east; and, while the latter have been at all times exposed to the vicissitudes of external revolution, and the greatly more important and radical change from the silent progress of natural colonisation, the recesses of the Highlands have ever proved the shelter and protection of the descendants of the older tribes of the country, and the limit to the advance of a stranger population. [Illustration: MAP SHEWING MOUNTAIN CHAINS _W. & A.K. Johnston, Edinburgh & London._ ] The territory which forms the modern kingdom of Scotland is thus thrown by its leading physical features into three great compartments. First, the districts extending from the Solway, the Cheviots, and the Tweed, on the south, to the Firths of Forth and Clyde on the north; secondly, the low country extending along the east coast from the Forth as far as the Moray Firth, and lying between the sea and the great barrier of the Grampians; and thirdly, the Highland or mountainous region on the north-west. [Sidenote: Mountain chains.] In each of these great districts natural boundaries are again found exercising their influence on the subordinate political divisions. [Sidenote: The Cheviots.] In the first of these great compartments, the lofty range of the Cheviots, which forms the southern boundary and presents a steep face to the north, extends from the Cheviot Hill on the north-east by Carter Fell to Peel Fell on the south-west; and from thence a range of hills, sometimes included in the general name of the Cheviots, separates the district of Liddesdale from that of Teviotdale, and has its highest point in the centre of this part of the island, in a group of hills termed the Lowthers, where the four great rivers of the Tweed, the Clyde, the Annan, and the Nith, take their rise. From thence it extends westward to Loch Ryan, separating the waters which pour their streams into the Solway Firth from those which flow to the north. From the centre of this range a smaller and less remarkable chain of hills branches off, which, running eastward by Soutra and Lammermoor, end at St. Abb’s Head, at the entrance to the Firth of Forth, separating the tributaries of the Tweed from the streams which flow into the Firth of Forth. In the centre of the island, a barren and hilly region divides the districts watered by the rivers flowing into the east sea from those on the west coast.