Geological Society of London. 45 



carries a vertical transparent scale divided and numbered to 360°, 

 and also with cross fibres which intersect at right angles. The 

 fittings and adjustments of the instrument are of such a character 

 that the camera can be accurately levelled and directed towards any 

 point in a horizontal direction, and when a photograph is taken in 

 an ordinary way the bearing of the median vertical plane, which 

 bisects the instrument through the photographic lens, will be re- 

 corded automatically on the face of the photograph. 



The vertical fibre (and its image on the photograph) serves as an 

 index to read the bearing ; and the same fibre marks, by its shadow, 

 a line right across the photograph, which marks the median vertical 

 plane on the image. 



The horizontal fibre is adjusted to mark on the image the hori- 

 zontal plane which bisects the photographic lens. 



The camei'a rests on a divided horizontal circle, which can be 

 adjusted to a truly horizontal position by levelliug-screws. There 

 is a tripod stand and head, with suitable appliances for supporting 

 and adjusting the instrument in position. The camera is provided 

 with a rectilinear doublet lens and iris diaphragm and rack-aud- 

 pinion focussing adjustment. It is made of aluminium, and it is 

 surmounted by a telescope adjustable in altitude and fitted with 

 vertical and horizontal webs ; and it is also surmounted by a 

 revolvable tubular level. 



The details of construction and the peculiar features and adjust- 

 ments of the instrument are fully described in the paper, and some 

 of the chief purposes to which it may be applied in furtherance of 

 geological research are pointed out. 



4. " The Marble Beds of Natal." By David Draper, Esq., F.G.S. 



A "crystalline limestone of enormous thickness" was mentioned 

 by Mr. C. L. Griesbach, in 1871 (Q. J. G. S. vol. xxvii. p. 5(^), as 

 occurring along the lower course of the Umzimkulu, in the county 

 of Alfred in the southern part of Natal. Since the time of his visit 

 there the country has been opened out by settlers, and some attempts 

 have been made to utilize this marble. The chief mass of this rock 

 is met with at about seven miles inland, in the Indwendwa hill- 

 range, within the fork formed by the junction of the Umzimkulu 

 and the Umzimkulana, over 700 feet above sea-level, and continuous 

 with the tableland westward. This consists of granite, overlain 

 with the massive marble, roughly stratified, which is denuded north 

 and south of the hill, into the gorges of the two rivers, and is 

 continued on the opposite flanks until cut off by faults. The north 

 fault divides it from the Table-mountain Sandstone lying on clay- 

 slate; and the south fault divides the granite from the Table-mountain 

 Sandstone and clay-slate. The bedding of the marble dips towards 

 the rivers on each of their flanks, and strikes E. and W. 



In quality the marble varies from coarse to fine-grained, and in 

 colour from pure white to deep red. The coarse-grained variety 

 contains 5 to 13 per cent, of carbonate of magnesia. Calcareous 

 tufa, in some places several feet thick, has been formed from the 

 marble. 



