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GEOLOGY sand deposits were succeeded by the finer mud of the Stockingford Shales, although the waters must have become sufficiently clear and calm at one time to have allowed of the formation of the Hyolite Limestone from the remains of various mollusca. The only fossils in the lower two divisions of the Quartzite are a few worm-burrows, sug- gestive of the sands having been deposited along a shore ; the Shales however as we have seen contain abundant evidence that the Cambrian seas were peopled with a considerable fauna. Intrusive Igneous Rocks. The volcanic activity which is evidenced by the igneous origin of the Caldecote rocks probably continued or was reopened probably in immediately post-Cambrian time ; for both the Hartshill Quartzite and especially the Stockingford Shales are traversed by many sills and dykes of diorite (camptonite), which are evidently solidified masses of molten rock forced up from below into the Cambrian sediments. There is no evidence whatever to show that these ever reached the surface and produced volcanoes, terrestrial or submarine. The sills and dykes generally follow the bedding, but frequently cut through the strata, baking and altering them. Yates perceived their intrusive character in 1824. Allport 1 gave a figure of a section showing this at Chilvers Colon railway cutting. Mr. Fox-Strangways 2 mentions that in the quarry south of Merevale church the Stockingford Shales dip at 1 5 to the south-west, while the igneous rock inclines at an angle of 35 in the same direction. The sheets of diorite vary from mere threads less than a foot thick to masses over a hundred feet through. They attain a great develop- ment in Merevale Park and at Chilvers Coton. They have been wrought for paving-cubes. One of the sills is well exposed in the Midland Railway Company's quarry at Nuneaton station ; the jointing of the rock is at right angles to the quartzite beds between which it was intruded and cooled. At the entrance to Messrs. Tyre's quarry a thin sheet of diorite intruded into the lower layers of the quartzite has segre- gated on cooling into basic clots and acid veins. The microscopic structure and composition of these igneous rocks have been described by Allport, Waller, Teall, and Watts ; it was Allport's recognition of the fact that these rocks differed from the Car- boniferous dolerites which gave an early hint that the Stockingford Shales were no part of the Coal Measures. They consist essentially of a triclinic felspar and hornblende, with some magnetite and apatite. Augite and olivine are sometimes present ; "and Professor Watts 3 remarks that the rocks would be appropriately called hornblendic, augitic, or olivine-bearing camptonites. That the intrusions are of pre-Coal- measure age might justly be inferred by their entire absence from those rocks ; but this was placed beyond doubt by the careful mapping of the Coal Measure base by Mr. Strahan, 4 who found that at Maw- 1 Quart. Journ. Geol. Sue. rxxv. (1879), 637. 2 'Geology of Atherstone, etc.,' Mem. Geol. Survey, (1900), p. n. 3 Proc. Geol. Assoc. TV. (1898), 395. 4 Geol. Mag. (1886), pp. 550, 551. 9