Vol. 57.] IGNEOUS ROCKS OF THE TORT WORTH INLIER. 269 



These indications, lie thought, point to the fact that 



' the Tortwortb traps are of the Caradoc [LlaudoTery] period,' and ' are, in 

 fact, contemporaneously effused traps, n'lost probably the fruit of 

 limited and repeated pressures on the interior liquid masses of the earth, 

 followed by solidification at small dfc])ths below, or even in part at the surface 

 of the sea-bed.' ^ 



Reference is made to the ig-neous rocks of the Charfield district 

 in the first of a series of papers on the Geology of the Bristol Coal- 

 field, read before the Bristol Naturalists' Society by Mr. W. W. 

 Stoddart in 1873. Rough sections are given which show an intru- 

 sive boss of greeustone. They are admittedly diagrammatic and 

 not drawn to scale, and they are unquestionably misleading. Thus 

 the altered Llandovery Beds are described as ' vesicular and amyg- 

 daloidal ' ! 



In Mr. H. B. "Woodward's Geological Survey Memoir on ' The 

 Geology of East Somerset & the Bristol Coalfields' (187t)), the trap- 

 rocks are briefly noticed, and Phillips's description of their nature 

 summarized. 



Sir Archibald Geikie devotes a short section to the ' Upper Silu- 

 rian (?) Volcanoes of Gloucestershire ' in his work on the ' Ancient 

 Volcanoes of Great Britain ' vol. i (1897) p. 238. He summarizes 

 the views of Weaver, Murchison, and Phillips, and adds the follow- 

 ing sentence : — 



'If, as seems probable, some of them [the trap-rocks] are really interstratified, 

 they form the youngest group of Silurian volcanic rocks in England, Scotland, 

 or Wales,' 



One of the excursions in connection with the Bristol Meeting of 

 the British Association (1898) was to Tortworth, and one of us 

 wrote in the excursion-guide (p. 9) as follows : — 



[The traps] ' undoubtedly constitute somewhat irregular masses, but their 

 limitation to the Upper Llandovery Beds, their general parallelism to the strike 

 of the strata, their often exceedingly vesicular structure, and the occurrence 

 of red ashy-looking beds in their neighbourhood, seem to lend support to the 

 view ado])ted by Phillips that they are of Upper Llandovery age, and not 

 subsequently injected as dykes.' 



It is thus seen that the leading authorities who have studied the 

 district reach somewhat divergent conclusions. According to Weaver, 

 the traps are interstratified with the sedimentary series ; Buckland 

 & Conybeare, followed independentl}"^ by Murchison, regarded them 

 as intrusive dykes injected subsequently to the deposition of the 

 Silurian strata ; while Phillips assigned them to an age contem- 

 poraneous with the beds in which they are included, and described 

 them as partly interstratified as lava-flows, and partly injected 

 among the sedimentary deposits. In Buckland & Conybeare's map 

 two bands of trap, roughly parallel, are marked. Weaver draws 

 seven or eight parallel bands in Michaelswood Chase (= Mickle 

 Wood) ; William Sanders and the officers of the Geological Survey 

 draw three or four bands. 



1 Mem. Geol. Surv. vol. ii, pt. i (1848) p. 195. 



u 2 



