284 Reports and Proceedings — 



Mr. Tiddeman remarked that the WouTitain Limestone was 3000 or 4000 feet thick 

 in the Lake-district, and in the Pennine Chain, at a distance of 15 miles, only 600 ft. 



3. " An Account of a Well-section in the Chalk at the North End 

 of Driffield, East Yorkshire," By E. Mortimer, Esq. Communicated 

 by W. Whitaker, Esq., F.GS. 



In this paper, which was in continuation of a former communica- 

 tion to the Society (Q. J. G. S. vol. xxix. p. 417), the author stated 

 that the well-section referred to passed through 7 feet of clay and 

 47 feet of chalk, the upper 3 or 4 feet of the latter very rubbly and 

 broken. The chalk was bedded in laminae of from xVin. to 16 in. 

 thick. From a depth of 20 feet downwards the well exposed many 

 nearly vertical partings running in all directions through the Chalk, 

 and the surfaces of the blocks thus marked out showed numerous 

 striae, such as were described in the author's former paper. These 

 striae were in most cases horizontal, but some surfaces showed them 

 at an angle of 45° to the horizon. The laminse of which the chalk 

 was composed were separated by layers of a softer substance like 

 Fuller's earth, containing 1-67 per cent, of organic matter, 7-05 per 

 cent, of oxide of iron, 10-23 per cent, of alumina, and 3480 per cent, 

 of silica. The author regards this soft substance as formed by the 

 disintegration of chalk, shells, etc., caused probably by the periodical 

 prevalence of great waves or other disturbances in the Cretaceous 

 sea. The effect of its formation he considers would be to check the 

 upward growth of the mass of chalk, which he now, as formerly, 

 ascribes to the direct secreting action of numerous zoophytes. In 

 support of this view he states that the surfaces of the chalk laminae 

 are more or less irregular, and not even as if produced by quiet 

 sedimentary deposition. The paper contained detailed analyses of 

 the chalk and of the soft partings. 



Discussion. — Prof. Hughes thought that the origin of the particular structure 

 referred to by Mr. Mortimer was a question for mineralogists and chemists, though 

 somewhat similar forms might be produced mechanically. He pointed out that its 

 occasional occurrence along fissures not in the line of bedding was quite conclusive 

 against its being in any way referable to the period of original deposition. As to the 

 more clayey bands, he considered the Chalk, though often composed in a great 

 measure of comminuted organisms, to be all sedimentary, and had therefore no diiB- 

 culty in explaining how more clayey matter might accumulate over various areas at 

 different times. 



Mr. Wiltshire mentioned that argillaceous bands extending over wide areas are to 

 be observed in the Chalk. 



Mr. Whitaker stated that clay bands occur near Beachy Head. He considered 

 that the argillaceous hands are not seen in hard chalk. The analyses given by the 

 author were of much value. 



Mr. Charlesworth remarked that the Yorkshire Chalk presents exceptional charac- 

 ters. The sponges found fossilized in it are silicified throughout, but the silica is 

 eonfined to the sponges, and does not invest them. 



Mr. Koch stated that near Nice the Dolomitic Limestone sometimes exhibits a 

 structure similar to that described in the paper, and that when this structure occurs, 

 minute crystals can be detected in the mass. 



4. "On Slickensides or Eock-striations, particularly those of the 

 Chalk." By Dr. Ogier Ward. Communicated by Prof. Morris, F.G.S. 



The author referred to previous communications on this subject, 



