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VIII. — The Lower Carboniferous Volcanic Rocks of East Lothian [Garlton Hills). By 

 Frederick H. Hatch, Ph.D., F.G.S., of the Geological Survey. Communicated by 

 Sir Archibald Geikie, F.K.S. (With Two Plates.) 



(Read 2nd May 1892.) 



PAGE 



Introduction : Physical Features of the District, 115 



Part I. The Lower, Basic Lavas, 116 



„ II. The Upper, more Acid Lavas, 119 



„ III. The Materials Filling the Vents, 122 



Summary, 125 



Introduction: Physical Features of the District. 



The rich agricultural tract of country that forms the north-western part of East 

 Lothian, undulating uniformly from the foot of the chain of the Lammermuirs towards 

 the Firth of Forth, swells near Haddington into the cluster of the Garlton Hills, and the 

 neighbouring masses of Traprain Law and North Berwick Law. 



The rocks that build up this elevated ground are lavas and tuffs that were produced 

 during the period of volcanic activity that characterised the deposition of the Lower 

 Carboniferous beds of Scotland. In East Lothian their eruption followed close on the 

 deposition of the sandstones and marls that constitute the base of the calciferous sand- 

 stone group.* 



Volcanic rocks of Lower Carboniferous age cover a considerable area in the Midland 

 Valley of Scotland. Thus they form the ranges of the Campsie Hills and Kilpatrick, as 

 well as the uplands of Renfrewshire and North Ayrshire. In all of these areas there is 

 an intimate relationship of petrographical types. But in the Garlton Hills we meet with 

 types not elsewhere developed. 



The stratigraphical relations of the rocks about to be described are somewhat obscured 

 by the nature of the ground. The main features are given in Sir Archibald Geikie's 

 classic paper on the " Carboniferous Volcanic Rocks of the Firth of Forth." t He 

 estimates the thickness of the volcanic series between the red sandstones and the base of 

 the Carboniferous Limestone at 1500 feet, though the estimate is stated to be only 

 approximate on account of the paucity of sections. At the base of this thick pile lies a 

 series of red and green tuffs, which can be well seen along the coast to the west of 

 Dunbar, and on both sides of North Berwick. " After the cessation of the showers of 

 ash and bombs, lava began to flow and continued to do so with little intermission until 



* A. Geikie, Trans. Boy. Soc. Edin., vol. xxix., 1880, p. 447. See also his Presidential Address to the Geological 

 Society, 1892. t hoc. cit. 



VOL. XXXVII. PART I. (NO. 8). T 



