^<^1« 57'] IGNEOUS EOCKS OF THE TORTWORTH INLIER. 267 



18. The Igneous Rocks and Associated Sedimentary Beds of the 

 ToRTWoRTH Inlier. By Prof. Conwy Lloyd Morgan, F.R.S., 

 E.G.S., and Prof. Sidney Hugh Reynolds, M.A., F.G.S. (Read 

 April 3rd, 1901.) 



[Plates X & XI.] 



Contents. 



Pa^e 



I. Introduction ...r.v.vv 267 



II. Description of the Exposures 270 



(«) The Oharfield-Green Exposures. 

 \b) The Avening-Green and Daniel's Wood Exposures, 

 (c) The Darcery, Mickle- Wood, and Middle-Mill Exposures. 

 III. The Petrology of the Igneous Rocks 279 



(a) The Oharfield-Grreen Exposures. 



(b) The Avening-Green and Daniel's Wood Exposures. 



(c) The Damery, Mickle-Wood, and Middle-Mill Exposures. 

 {d) Summary with regard to the Igneous Rocks. 



IV. Conclusions 284 



I. Introduction. 



The Silurian rocks of the Tortworth district in Southern Gloucester- 

 shire present several features of geological interest. Lying to the 

 north of the horseshoe ridge of Carboniferous Limestone, which 

 forms the rim of the Bristol Coalfield, they share in the synclinal 

 disposition of the Palaeozoic strata. They underlie the attenuated 

 Old Red Sandstone, which in this district is not more than some 

 200 or 300 feet thick ; but the exact relation of Silurian to Old 

 Red is nowhere clearly seen. The strata include beds of Ludlow, 

 of Wenlock, and o^ "''")per Llandovery age, the last-named being 

 originally regarded Jaradoc. The chief points of interest are : 

 (1) the remarkable attenuation, of the upper strata, the Ludlow 

 Beds not exceeding 100 feet in thickness, and the W^enlock attaining 

 a thickness of at most 700 feet, probably less ; (2) the limited 

 number of fossils recorded; and (3) the occurrence of igneous rocks 

 interbedded with the Upper Llandovery strata, and passing up to, or 

 perhaps just into, the Lower Wenlock Beds. It is with these igneous 

 rocks and their relation to the sedimentary beds that this paper deals. 

 The trap-rocks were carefully studied and described by Thomas 

 Weaver in 1819.^ He regarded it as 



'evident that the trap constitutes discontinuous beds included in and parallel 

 to the continuous series of the stratified transition -beds ' ; '^ 



but, as a faithful disciple of Werner, he hastened to add that, since 



these stratified beds were 



' undeniably aqueous products, I do not perceive how we can aroid extending 

 the same origin to trap also when found under similar circumstances.' 



^ Trans. Geol. Soc. ser. 2, vol. i, pt. ii, p. 317 ^ Ibid. p. 335. 



Q.J.G.S. No. 227. u 



