ON A PECULIAR FORM OF VARIEGATION IN CAMBRIAN SLATE. SIR, I send herewith a sketch of a rather unusual form of variegation occurring in a slab of Cambrian Slate. I observed it a short time back at Reading, but am not aware of the exact locality from whence the slate was obtained-probably, however, from the Penrhyn or Llanberis quarries. As it bears on the question of the causes that have induced the parti-colored banding of variegated rocks, you may perhaps give it a place in the MAGAZINE. The ordinary form of variegation of Cambrian Slates consists of mechanical nuclei and layers of interbedded matter concentrically environed by pale green slate, the bleaching of which has been due to the abstraction of the greater part of the colouring oxides of iron. In a paper contributed to the Geological Society (Quart. Journal of Geological Society, Nov. 1868), and a communication which appeared in the GEOLOGICAL MAGAZINE for March, 1868, I endeavoured to shew that this abstraction was independent of the mere mechanical washing-out in a soluble condition of the colouring oxides. The example represented in the accompanying engraving seems to support this view. Here we have not only a bleached zone immediately adjacent to the central nucleus, but a second concentric zone separated therefrom by an intervening band of unaltered slate. It is obvious that the positions of both the inner and outer pale zones have been determined in some way by the little mechanical nucleus, and if the discolorations were due to the mere solvent action of matter emanating from it, it seems impossible to account for the intervention of the unaltered zone entirely isolating the outer pale band from the inner zone and the central fragment of foreign matter. GEO. MAW. Quarter Actual Size. BENTHALL HALL, BROSELEY, November, 1869. SUCCESSOR TO THE LATE MR. JUKES.-Mr. Edward Hull, M.A., F.R.S., F.G.S., has been appointed Director of the Geological Survey of Ireland, and Professor of Geology in the Royal College of Science, Dublin, in the room of the late Mr. Jukes. Mr. Hull had not long before been chosen a District-Surveyor on the Geological Survey of Scotland. ERRATUM.-A serious erratum occurred in our November Number (after it had been sent to press). In shifting the form, a line of type -belonging to the Obituary Notice of Dr. Rubidge-was removed by the printer from the foot of p. 527, and inserted at the foot of p. 525, entirely destroying the sense of both the Obituary Notice and of Mr. R. Craig's Letter.-EDIT. BRA Brachiopoda, Liassic species of, 550. and W. Whitaker, On the Forma- Brodie, P. B., Geological notes on North- Brown, E., Waste of Rocks, 379. H. T., Absorption of Carbonic R., Coal-fields Pacific coast, 372; CALAMITES, Foliage and Fruits Calymene ceratophthalma, 37, 43. Canada, Geology of Hastings Co., 279. Carboniferous Limestone at Southerness, Depth of the Contortion of, 505. Organic Con- tents of Mineral veins in the, 563. CRU Caucasus, Geological notes on the, 120. Celestine in Egypt, 31. Chalk, Upper, Middle, and Lower, 164. Chesil Bank, Formation of the, 325, China, Geology of, 87. "Chips and Chapters," 363. Clark, G. T., Basaltic Dykes of India, Clarke, W. B., Dinornis an Australian Climaxodus, 381; C. ovatus, 42. 17, 18; of the North Pacific Coast, 372. Concretions, Banded and Brecciated, 529. Consumption Death-rate, Connection of Contortion of Mountain Limestone, Cope, E. D., Fossil Reptiles of North Coquand, H., Cretaceous Rocks of Europe Crag Mammalia, 47, 142, 143, 190, 237. CTE Ctenodus, 314, 317. Cycadean fruit, New genus of, 97. DAKOSAURUS, 27, 188, 367. Dakyns, J. R., Notes on the Geo- GEO Type Specimens of Fossil Fishes in Eophyton from Lower Arenig Rocks, 534. Equisetum, Fruits, of, 295. Eyton, C., "Geology of North Shrop- ARM REPORTS, 569. Geology and Palaeontology, 162, 199, Faults in Strata, 341. 251, 300. Dawkins, W. B., British Post-Glacial Dawson, J. W., Graphite of the Lauren- De la Touche, J. D., On the Measure- Denudation, 109, 191, 263, 347, 349, 465. of Western Brittany, 442. Devonshire, Geology of, 76. Diamonds, Discovery of, at the Cape of Dinornis, an Australian genus, 383. American, 565: New genus of, 573; Dollfus, A. and E. de Montserrat, Geo- logy of Guatemala and Salvador, 455. Duncan, P. M., Cretaceous fossils from Sinai, 31; Amphidetus and Breynia, 28. Ferns of the Coal-period, 291. Fossil, in the Devonian Rocks, 77. Floods in the Island of Bequia, 26. of Greenland, Miocene, 322. Submerged, of Barnstaple Bay, 77. List of, from the Skiddaw Slates, 498. Foster, C. Le N., Caratal Gold-field, 330. Furness, Notes on the south coast of, 286. ALWAY, Geology of the district Du Noyer, G. V., Obituary notice of, 93. G around, 567. ARTH, Internal Fluidity of, 145, 475, E 136, 174, 227, 283, 371. Royal Society of, 129. Crag, 190, 237; in the Red Crag, 143. Enniskillen, Earl of, Catalogue of the Gaudry, A., Palæontological Address, 75. Geikie, A., Address to Edinburgh Geo- J., Additional Note on the Dis- Geological Dynamics, 472. GEO Ireland, 567. Tables, 423. Time, 8, 472. Geologists' Association, 427. Glacial Climate, Cause of the, 331, 382. Glaciers in South Devon, 40. Glasgow Geological Society, 34, 182, 284. Gold-fields of Sutherland, 327; of Mount Graham, T., Relation between Palladium of Leinster, Albite in the, 561. Graphite of the Laurentian Rocks, 39,368. Greenland, Miocene Beds of, 174; Mio- Greensand, Upper and Lower, Springs Greenwood, G., Denudation of Norfolk, 45; Formation of the Chesil Bank, 523; Gyrodus, new species of, 366. HALL, M., Expedition of, 528. Harkness, R., Address to the Geo- and S. V. Wood, jun., Iutra- KIL Health, Public, and Geology, 79, 144, Hébert, E., Classification of the Cre- Heer, O., Miocene Flora of North Green- Helix, Supposed burrows of in Carbon- Hippopotamus in Post Pliocene Drift from the Kimmeridge Clay, 366; Ga- Hull, E., New Red Conglomerate of Hunstanton, Geological Excursion to, Hunt, J., Obituary notice of, 480. T. S., On the Probable Seat of Hutton, F. W., Extinct Volcano in New Huxley, T. H., Anniversary Address to ТCHTHYODORULITES, New species Igneous Rocks of the Lake-district, 370. Ireland, Geological Survey of, 567. JAVA, Stone Implements from, 125. Joass, J. M., Sutherland Gold-fields, 327. Judd, J. W., Origin of the Northampton Jukes, J. B., Obituary notice of, 430. ILMARNOCK, Bed of Sand with Hawkins, B. W., Restorations of; 3xtinct Keti Chels below the Boulder American Dinosauria, 565. clay at, 525. |