AND THE ADJOINING DISTRICT, BERWICKSHIRE. 37 



space, the breadth of which seems to he less in proportion to the bett&r preserva- 

 tion of the scale, and vice versa. Where organic remains are most abundant, the 

 strata are blanched in large irregular patches. In the centre of the spots a small 

 speck of protoxide of iron may be found, but this is generally so minute, as 

 not to be visible, unless the plane in which the spot is split passes through the 

 centre. 



The only decided vegetable remains found in Prestonhaugh, occur in some 

 beds of soft red sandstone, overlying the spotted strata above described. The 

 matrix in which they are embedded has been imfavom-able to their preservation, 

 so that they are obscurely marked, and when exposed to the weather for a short 

 time, become almost indistinguishable. They appear to be a sort of Algm. At 

 Cockburn mill, some slabs of rippled sandstone present markings in relief much 

 resembling fucoids, but shew no trace of carbonaceous matter, so that the vege- 

 table origin of these, though not unlikely, is at least doubtful. Great numbers of 

 the vermiform bodies before described are associated with these markings. 



The strata in Prestonhaugh containing the vegetable remains, are succeeded 

 by other beds of red and variegated sandstones and clays, marked with blanched 

 spots and ripples, and containing, at least, one stratum in which the remains of 

 the holoptychius are very abundant. Among these also occm- thin beds of coarse 

 sand, mixed with small rounded pebbles of white quartz, and presenting decided 

 indications of littoral deposition. A succession of red sandstones and clays, 

 which appear to have been deposited in deep water, follow, and may be traced 

 along the south bank of the Whiteadder to Preston bridge, where they are inter- 

 rupted by a large trap-dyke, accompanied by a very extensive fault or disloca- 

 tion. On the opposite side of this dyke the coal measures appear tilted up at 

 high angles, there being only the breadth of the dyke, which at this place does 

 not exceed 100 yards, between the two formations. In consequence of this dislo- 

 cation, and subsequent denudation, the upper beds of the old red sandstone, or 

 those which graduate into the coal measures, are awanting at this place, having 

 been entirely swept away on the west side of the dyke ; whUe, on the east, they 

 are buried beneath a great thickness of the coal measures. 



The transition rocks thus removed or thrown down at this place, are pretty 

 well developed in other parts of the county ; as in the course of Langton burn, 

 about two miles SW. from Dunse, and in that of the Blackadder above Fogo. 

 They consist of thick beds, of a coarse, arenaceous, concretionary limestone, or 

 cornstone, with which are associated beds of shale and clay, also impregnated 

 with a considerable quantity of calcareous matter ; and as regards colour and 

 general aspect, blending the characters of the argillaceous strata of the old red, 

 and the shales of the coal measures. They appear to be destitute of organic re- 

 mains, either animal or vegetable, and exhibit no appearances of ripple marks 

 or blanched spots. 



VOL. XVI. PART I. K 



