304 G. W. Tyrrell — Bekinkinite of Barshaw, Renfrewshire. 



river drainage. It is perhaps as well to continue on this line of 

 inquiry. As is well known, the Pennine Fault throws down in 

 a westerly direction and the Tindale Fault throws to the north. 

 Should these two Faults intersect, there would be four fault faces at 

 this intersection, and supposing the Mesozoic and Glacial deposits 

 were removed we should see the south-east solid angle standing 

 higher than the three others, while the north-western one would be 

 the lowest of all through being thrown down by both faults. The 

 depth at which the Palaeozoic rock surface lies is not known, yet it 

 is probably not so great as where it troughs under the Cumberland 

 Plain and under the Solway. 



Whatever the position of this old surface may have been in the 

 past, we know that it is now buried under Mesozoic deposits. As 

 these deposits were formed upon it, they would follow its general 

 contours, their degree of dip having a tendency to lessen as they 

 increase in thickness. When later movements set in, these deposits 

 would still retain their parallelism with this buried surface. As 

 a result of this, the present-day drainage system should be similar to 

 that which would be formed upon this surface were the younger rocks 

 removed and the land raised so as to be above sea-level. (Fig. 8.) The 

 contour-lines of this surface would sweep round to the north-west on 

 leaving the Tyne area and run towards the Cheviots. This change 

 in direction on leaving the main valley of the Tyne would produce 

 a watershed running in a northerly direction between the tributaries 

 to the North Tyne and to the Eden from the north-east. As a result 

 of this watershed and the westerly slope of the trough towards the 

 Solway, no rivers would flow out of the Eden area into the Tyne area 

 across the Pennine fault. 



The configuration of the present drainage area of the Eden agrees 

 very well with the construction above given, and therefore supports 

 the mode of origin of this part of the Tyne watershed, the irregularities 

 •of which, as also in the other parts, are caused by later denudation 

 producing sinuosities in its direction across country. 



(To be concluded in our next number.) 



III. — The Bekinkinite of Barshaw (Renfrewshire), and the 

 Associated Pocks. 1 



By G. W. Tyrrell, A.B.C.Sc.,F.G.S., Lecturer in Mineralogy and Petrology, 

 University of Glasgow. 



Introduction. 



rMHE recognition of teschenites in the Midland Valley of Scotland, 

 J_ first by Teall 2 and later by several other petrographers, has led 

 to the discovery of numerous varieties of analcite-rich rocks in the 

 same area. 3 One of the most interesting of these is the unique rock 

 discovered in an old quarry at Barshaw near Paisley, during the 

 remapping of the district by the officers of the Geological Survey of 



1 This paper forms part of the results of a research which has been aided by 

 a grant from the Government Grant Committee of the Eoyal Society. 



2 British Petrography, 1888, p. 359. 



3 Tyrrell, Geol. Mag., Dec. V, Vol. IX, pp. 69-80, 120-31, 1912. 



