1868.] MAW VARIEGATED STRATA. 353 



reconversion of the sesquioxide into bisulphide by the action of sul- 

 phuretted hydrogen produced in the decay of organic matter, and 

 supposes that a discharge of colour may also have been due to the 

 acids produced in the putrefaction and decay of moist vegetable 

 matter. 



Dr. Sterry Hunt, in a paper on '' Chemical Geology," read before 

 this Society, June 5th 1859, and published in vol. xv. of the Quar- 

 terly Journal,p. 488, also supports the view of Dr. Dawson, that the 

 elimination of iron from some sedimentary strata is due to the re- 

 duction of the sesquioxide to a soluble protoxide by the action of 

 organic matter. 



Mr. H. C. Sorby, in a paper on the origin of slaty cleavage, in the 

 * Edinburgh New Philosophical Journal ' for July 1853 (p. 3), in- 

 cidentally refers to the bleaching of slates, and attributes the forma- 

 tion of the pale blotches to " concretions of a peculiar kind formed 

 round bodies lying in the plane of bedding." 



Mr. H. C. Sorby, in a paper in the * Proceedings of the Geologi- 

 cal and Polytechnic Society of the West Riding of Yorkshire ' for 

 1856-57, ^' On the Origin of the Cleveland Hill Ironstone," describes 

 the replacement of carbonate of lime by carbonate of iron in shelly 

 limestone from the Inferior Oolite — a process which will have to be 

 referred to as a probable agent in the production of a peculiar form 

 of variegation in the Northamptonshire Oolites, 



Mr. Pengelly, in a paper on the '* Red Sandstones, Conglomerates, 

 and Marls of Devonshire," read before the Plymouth Institution and 

 Devon and Cornwall Natural History Society, March 19th 1863, 

 and published in the ^Transactions' of that body for 1862-63, 

 pp. 15-38, dissents from the conclusions of Dr. Dawson, that the 

 colour of red beds is the result of a secondary process, and enters 

 minutely into the circumstances of the variegation of the red beds of 

 Devonshire. To this valuable memoir I shall have occasion further 

 to refer in the body of the paper. Although the author expresses no 

 definite conclusions, I believe the facts pointed out for the first time 

 by Mr. Pengelly are suggestive of the true explanation of many of 

 the phenomena of variegation, and, I may add, agree with the views 

 I suggested in the paper read last year before the Society, although 

 I was not at the time aware of several of the facts Mr. Pengelly had 

 recorded. 



In a paper on the " Chemistry of some Carboniferous and Old 

 Red Sandstones," read by Mr. J. W. Young before the Geological 

 Society of Glasgow in March 1867, the light blotching of Red Sand- 

 stones is attributed to the presence of some organism in the sand, 

 the decomposition of which has reduced the sesquioxide to protoxide 

 of iron, which would be subsequently removed as carbonate by water 

 containing carbonic acid percolating the mass; and reference is 

 made in this paper to an observation by Mr. James Bennie, " that 

 sand in contact with decaying roots or twigs is often found to be 

 partially bleached." 



The paper by Mr. Edward Davies, of Liverpool, on the '^Action of 

 heat or ferric hydrate in presence of water," at p. 69 of vol. iv. (new 



2c2 



