92 Reports & Proceedings — Geological Society of London. 



he was not aware that the method had beeu successfully applied to 

 small objects, such as Foraminifera. After he had begun his 

 experiments he found that M. Pierre Goby had done some work in 

 this direction in France, but the method as he described it is 

 surrounded with considerable mystery and elaboration of apparatus, 

 which appear quite unnecessary. The speaker's results were arrived 

 at independently ; in fact, they are really a side issue. 



His original experiments were directed rather towards the use of 

 X-rays in obtaining magnified images, altogether apart from the 

 usual skiagraphic methods in which a shadowgraph is, in fact, all 

 that can be produced. The primary object has not yet been achieved, 

 although there is some reason to hope that it may ultimately come 

 to pass. The results shown by Mr. Heron- A Hen are obtained by 

 quite simple means. A very narrow beam of X-rays, such as would 

 be termed "a parallel beam" when speaking in terms of ordinary 

 light, is allowed to impinge on the object, the latter being in contact 

 with the photographic plate. The negative produced is, therefore, 

 of the same size as the object. Photographic enlargement is then 

 resorted to, and the result had been shown on the screen. There are 

 two points to which careful attention is required if success is to be 

 achieved. 



The quality of the X-rays must be suited to the object. In nearly 

 all cases of small objects, what are known as " soft " X-rays must be 

 used, and the degree of softness is the crux of the whole matter. 

 The photographic plate must be oi exceedingly fine grain, otherwise 

 the amount of enlargement that can ba obtained is very limited. 

 Difficulties in this direction have been overcome, and Mr. Heron- 

 Allen has stated that the results are of considerable biological value. 



Dr. A. Smith Woodward, F.K.S., V.P.G.S., exhibited a radiogram 

 of the original slab of lithographic stone containing the skeleton of 

 Archceopteryx, made for the British Museum by Dr. Robert Knox in 

 1916. It was evident that the penetrability of the fossil bones to 

 the X-rays was the same as that of the surrounding matrix. The 

 only portions of the skeleton visible in the radiogram were those 

 more or less raised above the general surface of the slab. This i-esult 

 accorded with that obtained bv Professor W. Branca when he 

 similarly experimented with the Berlin specimen of Archmopteryx. 



2. December 19, 1917.— Dr. Alfred Barker, F.E.S., President, 

 in the Chair. 



The following communication was read : — 



" The Chellaston Gypsum-Breccia considered in its relation to 

 the Gypsum-Anhvdrite Deposits of Britain." By Bernard Smith, 

 M.A., F.G.S. 



This communication is designed to clear up some of the ambiguities 

 that have arisen with regard to the actual mode of formation of the 

 deposits of gypsum in Britain — cliiefly from the point of view of 

 the field observer. An attempt is made also to show the true 



