Vol. 70.] ACID AND OTHER INTRUSIONS NEAR MELROSE. 303 



12. Acid and Intermediate Intrusions and Associated 

 Ash-Necks in the Neighbourhood of Melrose (Rox- 

 burghshire). By Rachel Workman aIcRobert, B.Sc. 

 (Communicated by E. B. Bailey, B.A., F.G.S. Read 

 February 25th, 1914.) 



[Plates XLI-XLIII.] 



Contents. 



yfPage 



I. Introduction 303 



II. Relation to the Upper Old Red Sandstone . . . 304 



III. Laccolites and SiUs 305 



IT. Dykes ! 310 



V. TheNecks 312 



VI. Summary 313 



I. Introduction. 



The io'neous rocks under consideration fall within an area about 

 7 miles square, included in Sheet 25 of the Geological Survey's 

 1-inch map of Scotland. 



It is generally believed that they date from a late period in 

 the history of the ' Plateau Eruptions ' of Calciferous Sandstone 

 times, and correspond with the trachytic lavas and intrusions 

 of the Garleton Hill district (East Lothian), and with the similar 

 intrusions in the Campsie and Renfrewshire hills. The only 

 new evidence obtained, bearing upon this suggestion, weakens 

 rather than supports it : a small neck, the Little Hill, including 

 ash and plugged by basalts of two types, has been found within 

 the Eildon complex of felsitie and trachytic rocks, and is almost 

 certainly of subsequent origin. But it should be borne in mind 

 that the admittedly-late felsitie and trachytic intrusions of the 

 Campsie Fells are in certain cases cut by still later basalts. 



The restricted area over which acid rocks of this suite extend 

 in the various districts of Scotland in which they occur is partly 

 due to extreme denudation, and partly to the viscous character 

 of their magma. Only in the Garleton Hills are extensive lava- 

 flows preserved. It seems fairly certain to me that Dr. Peach is 

 right in regarding none of the Melrose rocks as lavas, although 

 the evidence does not altogether exclude the possibility of lavas 

 entering into the Eildon complex. 



The rocks may be grouped, according to their field-relations, as 

 follows : — 



Laccolites and sills. — White Hill; Black Hill; Bemerside ; Eildon 

 Hills ; Bowden Moor Quarry ; Whitelaw Hill. 



.Dykes mostly trending north-eastwards. — Several are strung- 

 through the country between Melrose and Selkirk ; two north-west of 

 Earlston. 



Necks. — Chief swood ; Little Hill, described here, although in the main 

 basaltic ; a small neck with trachyte, in a little gorge between Bowden Moor 

 Quarry and Rhymers Glen ; Faldonside Moor ; a small neck on the banks of 

 the Tweed, not visited. 



Q. J. G. S. No. 279. y 



