760 REPORT — 1893. 



of quartz into augite, the supply of the free silica possibly affecting the rock in 

 other ways as to its composition, not so easily demonstrable as the one here 

 described. 



This is one more fact which goes to show that igneous rocks are markedly modi- 

 fied in their composition by the rocks they traverse. I have pointed out elsewhere 

 that it is not a case of simple fusion or fluxion but rather one of selective diffusion. 



11. On the Gypsum Deposits of Nottinghamsldre and DerlysMre. 

 By A. T. Metcalfe, F.O.S. 



The gypsum deposits of Nottinghamshire and Derbyshire belong to the Keuper 

 series (Triassic). The ' Upper ISIarls,' in which the gypsum deposits occur, con- 

 sist of beds of marls with minor bands of sandstone. Rock salt is apparently absent 

 in both counties, but gypsum is abundant. 



The chief gypsum works in Nottinghamshire are at Newark, Orston, Barton, 

 Thrumpton Gotham, and Kingston, and in Derbyshire at Chellaston and Aston. 

 The gypsum varies in thickness from a mere film to fifteen feet or so, and occurs iii 

 the marls in the form of ' bowls,' ' cakes,' beds, and thin bands or veins, and 

 in every degree of purity. The more massive portions are usually saccharoidal or 

 amorphous, and the purest kiud is by the trade termed ' Superfine.' The tough 

 variety, commonly called ' Alabaster,' which is worked up into ornaments, is found 

 only in the Chellaston district. The thin bands or ' rivings ' are fibrous (' satin 

 spar '). These gypsum deposits were probably foi-med in salt lakes or inland seas, 

 similar to the Dead Sea and the Great Salt Lake of Utah. 



After extraction gypsum is cleaned, ground down to flour, and burnt. The 

 burning drives ofl" the combined water. When ground down to flour and properly 

 burnt gypsum possesses the valuable property of recombining with water, and 

 setting from a thin paste into a solid mass. The mineral thus treated forms 

 plaster of Paris, and is an ingredient in Keene's and other hardened cements. 



12. Report on Photographs of Geological Interest. — See Reports, p. 473. 



13. On a Bed of Oolitic Iron-ore in the Lias of Eaasay, 

 By Horace B. Woodwakd, F.G.S. 



[Communicated by permission of the Director-General of the Geological Survey.] 



The author drew attention to the occurrence in Raasay of a bed of oolitic iron- 

 ore which had not been previously noticed. The bed in question attains a thick- 

 ness of five feet, and lies at the top of the Middle Lias, beneath the dark shales of 

 the Upper Lias. The straligraphical position is thus approximately the same as- 

 that of the Cleveland iron-ore, although in Yorkshire the upper part of the Middle 

 Lias contains a series of ironstone bands. 



An analysis of the Raasay ore, made by Mr. A. B. Dick, showed in the grey 

 (unweathered) rock 29 per cent., and in tlie brown (weathered) rock 37 per cent., 

 of metallic iron. The discovery of the iron-ore was made during the progress of 

 the Geological Survey. 



14. Note on a Transported Mass of Chalk in the Boulder Clay at Catworth 

 in Huntingdonshire. By A. C. G. Cameron, Geological Survey. 



[Communicated bj' permission of the Director-General of the Survey.} 



In this paper the author comments upon the abundance of chalk fragments and 

 boulders that culminate in the Drift around the highest points in the county west 

 of the town of Huntingdon. At particular elevated spots there are outcrops of 

 white Chalk which are dug up and used about the farmyards, where it sets hard. 



