326 DR. A. M. DAVIES AND ME. J. DEINGLE OX [June I913, 



less than 0*1- mm. to 0-2 mm. ; (3) larger olivine-pseudomorphs, 

 idiomorphic, but with much parallel growth and large inclusions of 

 groundmass : these vary in length from 0*4 mm. up to 1 mm. ; 

 they consist almost entirely of dolomite or magnesite. There is- 

 no recognizable pyroxenic constituent. (See PI. XXXIII, fig. 4.) 



As the contact with the shales is approached, the groundmass 

 becomes perfectly isotropic. In an enclosure within an olivine- 

 pseudomorph its structure can be most easily made out : here 

 it consists of a colourless glass full of little brown translucent 

 isotropic granules, of uniform size (rather larger than 1 /x). In 

 the general groundmass there aro two sizes of granules, the larger 

 being about the size of the above but less translucent, and the 

 smaller forming an immeasurably fine dust. There are also seen 

 numerous oval structures which appear to be sections of ellipsoids 

 lying with their long axes not quite parallel to the contact-surf ace 

 (average dimensions, about 12 jj. x 9 p.). These are outlined by 

 a ring of the larger granules ; they have a very faint green tint, 

 u somewhat radial structure, and show the optical characters of 

 chlorite. I can only interpret them, somewhat doubtfully, as 

 elongate vesicles filled with secondary chlorite. Some others, of 

 almost exactly similar appearance, are composed of dolomite or 

 magnesite, while yet others are quite isotropic. (See PI. XXXIII, 

 figs. 5 & 6.) 



These sills show no close resemblance to any of the igneous 

 rocks of the Nuneaton district. They are more nearly paralleled 

 by some of the andesitic olivine-basalt sills in the Malverns, 1 

 particularly one intrusive in the Black Shales of Pendock's Grove 

 (31 102 of Prof. Groom's collection), and less closely by one in the 

 Black Shales of White-Leaved Oak (31 119) and one in the Grey 

 Shales of Bronsil (31 249). 



Even from the nearest of these the Calvert sills differ in the 

 following characters: — (1) The much finer grain of the ground- 

 mass ; (2) the absence of an}- recognizable pyroxenic constituent ; 

 (3) the greater abundance of olivine-crystals and of the larger 

 felspar-laths ; (4) the much greater amount of dolomite or 

 magnesite, and the very small amount of serpentine in the olivine- 

 pseudomorphs. 



(2) The Western Boring. 

 [J. P. & A. 31. D.] 



As nearly as can be determined, this boring is situated about 

 370 yards due west of the other. It was started, not at the 

 natural ground-level, but at the bottom of an excavation about 

 70 feet deep, the measured difference of level between the two 

 sites being 67 feet 8 inches. The log of the original boring made in 

 1904-1905 has already been printed - ; and, as the descriptive terms 



i T. T. Groom, Q. J. GL S. vol. lvii (1901) pp. 156-84. 



2 'Iron & Coal-Trades Review ' September 1st, 1911, pp. 316, 317. The 

 statement therein that the brickworks excavation is 90 feet deep is taken 

 from the log, and was probably a bad guess. 



