[Illustration: Fig. 246.--Branching portion of the great Dyke near Hawick (length about one mile).] [Illustration: Fig. 247.--Branching Dyke at foot of Glen Artney (length about four miles).] The Cleveland dyke, which in so many respects is typical of the great solitary dykes of the country, has been traced for many miles without the appearance of a single offshoot of any kind. Yet here and there along its course, it departs from its usual regularity. As it crosses the Carboniferous tracts of Durham and Cumberland, there appear near its course lateral masses of eruptive rock, most of which doubtless belong to the much older "Whin Sill." But there is at least one locality, at Bolam near Cockfield, in the county of Durham, where the dyke, crossing the Millstone Grit, suddenly expands into a boss, and immediately contracts to its usual dimensions. Around this knot several short dykes or veins seem to radiate from it. The dyke has been quarried here, and its relations to the surrounding strata have been laid bare, as will be again referred to a little further on.[191] [Footnote 191: This locality was well described by Sedgwick, in his early paper on Trap-Dykes in Yorkshire and Durham, _Trans. Cambridge Phil. Soc._ ii. p. 27.] Among the great persistent dykes of Scotland the absence of bifurcation and lateral offshoots offers a striking contrast to the behaviour of the dykes in those districts where they are small in size and many in number. But exceptions to the general rule may be gathered. Thus the Eskdale dyke is flanked at Wat Carrick with a large lateral vein, which is almost certainly connected with the main fissure. The Hawick and Cheviot dyke splits up on the hill immediately to the east of the town of Hawick, sends off some branches, and then resumes its normal course (Fig. 246). Again, one of the two nearly parallel dykes which run from Lochgoilhead across Ben Ledi into Glen Artney bifurcates at the foot of that valley, its northern limb (about two miles long) speedily dying out, and its southern branch throwing off another lateral vein, and then continuing eastward as the main dyke (Fig. 247).