THE 



GEOLOGICAL MAGAZINE, 



No. CIX.— JULY, 1873. 



OI^IC3-I^^.A.XJ ^^liTIOXjIES. 



I. — 'On the Occurrence of a Quartzite Boulder in a Coal-seam 

 IN South Staffordshire.^ 



By Rev. T. G. Bonney, M.A., F.G.S., 

 Fello-w and Tutor of St. John's College, Cambridge. 



INTEERUPTIONS in the continuity of a Coal-seam, whether in 

 the form of intercalated layers of sand or shoals of clay, are not 

 rare ; but I have been able to find little on record concerning the 

 occurrence of pebbles of any considerable size, except where there 

 was reason to suppose that the miners had struck upon an old river 

 channel. The Boulder, which forms the subject of this paper, was 

 found in the 13th Coal of the sinkings belonging to the Cannock 

 and Eugeley Colliery Company ; and I am indebted to the kindness 

 of its manager, E. C. Peake, Esq., for the opportunity of exhibiting 

 the specimen and for much of the following information. The seam 

 occurs at a depth of about 540 feet from the surface of the ground ; the 

 Boulder was completely enveloped in the coal, but its precise distance 

 from the top of the seam was not ascertained. This 13th coal is 

 considered to be identical with the 12th coal in the Brereton Colliery. 

 In the latter colliery this seam is about 135 feet above the lowest or 

 15th coal; and by boring to a depth of 68 feet, red rocks were 

 reached, which very probably, like those detected in the sinkings at 

 Halesowen, belong to the passage-beds between the Silurian and 

 Old Red Sandstone. 



The Boulder is in shape subspheroidal ; having been probably once 

 a rhombic parallelepiped, defined by joint planes whose angles have 

 since been worn away. Its girth in two directions at right angles is 

 about 19 inches, and its greatest thickness about 4 inches; it weighs 

 13 lbs. 13^ oz. The rock is a very compact and highly altered pale 

 grey quartzite, with a sharp almost conchoidal fracture ; lines on the 

 exterior roughly parallel to its flatter ends probably indicate divisional 

 planes due to original stratification. Lithologically it resembles very 

 closely one of the varieties of quartzite which is very common in the 

 Bunter pebble-beds of the neighbourhood. 



Two questions at once present themselves with regard to this 

 Boulder— (1) How did it come, (2) whence did it come, into the 

 position in which it was found ? 



(1). The absence of other pebbles shows that a stream alone 

 even in flood-time, is not likely to have brought it. For a torrent 



1 Eead before the Cambridge Philosophical Society, March 3, 1873. 



VOL. X. — NO. CIX. 19 



