lo PROCEEDINGS COTTESWOLD CLUB 19 lo 



A visit to the Windmill-Hill Quarry, Mr Boon's, completed the day's 

 work. 



The remarks on the geology made during the day may be thus sum- 

 marised : — 



The oldest known rocks have been termed " Archaean." Of them, three 

 divisions can be made : first and lowermost, the Malvernian (crystalline) ; 

 second, the Uriconian (volcanic); and third, the Longmyndian (predomin- 

 antly sedimentaries). Here and there doubtless the volcanic episode was 

 prolonged into Longmyndian times, but the products of volcanic activity are 

 the most obvious in the inter-Malvernian-Longmyndian or Uriconian period. 



Archaean rocks appear at the surface in six places in England, namely, 

 (i) in the Lizard district of Cornwall, (2) the Malvern Hills, (3) the Long- 

 mynds, (4) the Lickey Hills, (5) the Nuneaton-Atherstonc Ridge, and in (6) 

 Charnwood Forest. 



The Cotteswold Club had paid \isits to the districts numbered 2, 3, 4 and 

 6, but not to tho'^e numbered i and 5. The object of the Nuneaton excursion, 

 therefore, was to visit the latter — number 5. 



A section across the Nuneaton-Atherstone ridge at about half-way 

 between these two places reveals, at the south-eastern end, Triassic beds 

 faulted against pre-eminently volcanic rocks (see fig. i). 



These latter are succeeded unconformably to the west by the highly-in- 

 clined quartzites of Cambrian age, that in turn give place to the shales of the 

 same system (all invaded by sills and dykes of diorite,' with occasional con- 

 temporaneous flows), and overlaid at Chapel End by the less-inclined gritty 

 beds of the Lower Coal-Mcasures of the East Warwickshire Coalfield. 



The depressed Triassic rocks on the eastern side of the fault-line give 

 rise to an undulating lowland ; the Cambrian Quartzite to a marked but 

 quarried ridge ; the Cambrian Shales, with associated igneous rocks, to 

 a tract of parallel valley and irregular ridging ; while the less-inclined Car- 

 boniferous rocks slope regularly down and originate the features that one 

 expects to meet with in a well-formed coal-basin. 



It is only of recent years that the stratigraphic facts detailed above have 

 been discovered. Sir .\ndrew Ramsay saw in the Cambrian Quartzites a 

 well-developed Millstone-Grit, and in the black shales of the upper portion of 

 the Cambrian the unproductive beds of the Coal-Measures, thereby not fol- 

 lowing the more correct conclusions of his predecessor in the same field 

 of work, the Rev. James Yates, who in 1829 correctly paralleled the 

 Nuneaton volcanic and quartzite beds with the Wrekin and Caradoc series of 

 central Shropshire. Prof. C. Lapworlh and the late W. J. Harrison, however, 

 worked out the succession in the Nuneaton district, proving the I're-Cambrian 

 age of the volcanics now called the Caldecote series, and the Cambrian age of 

 the succeeding quartzites and overlying shales. Their work has been 

 accepted by the Geological Survey, and satisfies the very pleasing te;-.t, that 

 its results are in harmony with those obtained elsewhere, and this emphasizes 

 the simplicity of an at first sight highly complicated succession of beds. 



A fault forms the eastern boundary to the ridge. It might be thought 

 that its displacement was great, but the fact that in the quarry close to the 

 railway station the red marls (Kcuper) are seen resting upon the weathered 

 surface of the Quartzite necessitates a more moderate view being taken. The 

 Quartzite ridge of Nuneaton-Atherstone is one of several that represent the 

 higher portions of the old Mercian Highlands — uplands of .\rcha:an and 

 Palaeozoic rocks that long formed the high ground in our Midland Counties, 

 until they were obliterated under the thick deposits of Triassic date. So at 



I As it occurs in sills and dykes, this " diorite" is not " diorite," in the true sense of the word, 

 being a hypabyssal, instead of a plutonic, rock. For dyke-rocks, Rosenbusch uses the term " Lam- 

 prophyres," and those that are mainly composed of plagioclasc and hornblende are called 

 " camptonites." A camptouite is thus the hypabyssal equivalent of the plutonic rock, diorite. 



