Mr. WiNCB on the Geology of the Banks of the Tweed. 119 



In the bed of the rivulet called Firebourn (jsee Map, No. 3.)j ^ slip or 

 dyke is worthy of notice ; in the language of miners, it casts up to the 

 east, and the thin strata of Limestone and indurated Marl, before men- 

 tioned, may be seen in the water-course, dipping at an angle of 40° in that 

 direction. On the banks of the river, at a trifling distance lower down, 

 another slip divides the rocks, and brings two beds of micaceous Sand- 

 stone into contact with the calcareous series ; the upper of these Sandstone 

 beds is slightly tinged red, owing to its Mica being oxidated, but the 

 lower is of a pale yellowish-brown colour, and ambiguous character, 

 rather resembling a Coal Sandstone ; their aggregate thickness, with a 

 thin micaceous parting, is fourteen feet. Half a mile below Firebourn 

 there is a ford across the Tweed, noted in border history ; its direction 

 is south east, and may have been occasioned by the dyke. On the south 

 side of the river the ruins of Wark Castle (^ee Map, No. 4.) stand on an emi- 

 nence sixty feet high, composed of calcareous strata, similar in every re- 

 spect to those at Spring Hill, but their dip is in an opposite direction. 

 These impure Limestones seldom exceed a foot in thickness, and Gyp- 

 sum is interspersed through them. At about a hundred yards west of 

 the Castle, rocks of Dolomite again crop out on the banks of the river, 

 but to the eastward this peculiar mineral was no more to be seen ; nor 

 could I thoroughly satisfy myself as to its geological position, though I 

 have every reason to believe that it rests upon the Basalt, and suspect this 

 rock belongs to the same bed as occupies the north shore of the Tweed at 

 Carham, and is here again brought to the surface by the Firebourn Dyke. 



Again, passing to the north side of the Tweed, near the Temple at the 

 Lees (5ee Map, No. 5.), eight alternations of the same calcareous beds as 

 form the cliffs at Spring Hill and Wark, (except that the lower stratum 

 of Limestone contains very minute bivalve shells filled with Calcareous 

 Spar,) occupy the bank and the bottom of the river; their thickness 

 above ground is about ten feet, and their dip towards the north-west. 

 No strata of this description were again noticed for nearly six miles, and 

 when again seen, were found associated with Red Sandstone, in the vi- 

 cinity of Norham. 



