XX PREFACE. 



breadth as we approach the mouth of the Tweed. The princi- 

 pal rocks of this Formation (as it occurs in Berwickshire at 

 least) are sandstone and sandstone slate, indurated marl, a 

 coarse kind of limestone, and thick beds of conglomerate. In 

 general appearance, it bears some resemblance, at first sight, 

 to the Coal Formation; but is evidently more recent in its 

 date, and more mechanical in its structure. The predominat 

 ing and characterizing rock is the sandstone, which is soft, 

 friable, and variegated in its colour. The town of Berwick is 

 built on this formation, and, we believe, what are called the 

 Liberties of Berwick, are all included in it. At the mouth of 

 the Tweed, near Berwick Pier, we have an excellent opportu- 

 nity of noticing the characters of this formation, the succession 

 of its rocks, and the disposition of its strata. The principal 

 rock there is still the sandstone, containing numerous impres- 

 sions, principally of tropical plants.* This formation is con- 

 tinued southward under the bed of the Tweed : at a short dis- 

 tance from which, it is succeeded by the Coal Formation of 



Northumberland. Ascending the course of the Tweed, we 



behold, for many miles, on each side of the river, a display of 

 nearly the same rocks as those observed at its mouth, sand- 

 stone still being the predominating substance. The sandstone 

 almost always is found forming the bed of the river, the rest 

 of the banks being generally alternations of sandstone slate, 

 indurated marl and conglomerate, the last being of a very re- 

 cent and mechanical aspect (consisting of the same substances 

 which still compose the channel of the river), and usually oc- 



* The coarse limestone, however, consists almost entirely of bivalve shells., 

 echini, and corallines. 



