Alexander Bryson on Pholas-borings. 73 



nsroTiciES OIF iiyniEiMiozi^s. 



I. — The Geology of the Carbonifekous Books North and 

 East of Leeds, and the Permian and Triassic Eocks about 

 Tadcaster. By W. T. Aveline, A. H. Green, M.A., J. E. 

 Dakyns, M.A., J. C. Ward, and E. Eussbll. 1870. 8vo. pp. 14. 

 (London : Longmans & Co.) 



THIS little work is an explanation of quarter-sheet 93 S.W., of 

 the one-inch Geological Survey Map of England, portions of 

 which area have, we presume, been surveyed by each of the authors 

 therein mentioned. They give a brief sketch of the leading geo- 

 logical and physical features of the country, reserving all details for 

 a promised memoir on the Yorkshire Coal-field. 



The strata represented are the Millstone Grit, the Lower Coal 

 Measures or Canister Beds, the Middle Coal Measures, Magnesian 

 Limestones and Marls of Permian age, and the Bunter Sandstone. 

 Glacial deposits in the shape of Boulder-clay, Gravel and Sand lie 

 here and there, and Eiver and Estuary deposits likewise occur in 

 places. 



The authors furnish a table of the Carboniferous rocks shown in the 

 area, marking the maximum, minimum, and average thicknesses of 

 the different beds, with the local names under which they are known. 

 They point out those which are applied to economic purposes, in this, 

 as well as in the other series of rooks to which they refer. 



II. — On the Boring of the Pholadid^. 



The following notice on the Boring of the Pholadid^, by the late 

 Alexander Bryson, Esq., President of the Eoyal Physical Society, 

 extracted from the Edinburgh Philosophical Transactions (1859, p. 

 321), will be read with interest as bearing upon the Pholas-origin of 

 certain perforated Limestones. 



In this communication the author referred to the various theories 

 advanced to account for the boring of the Pholadidse in rocks. 



The first hypothesis, which supposes that the molluscs perforate 

 by means of the rotation of the valves acting as augers, he disproved 

 by exhibiting old individuals of the Pliolas crispata with the dentated 

 costse on the shells as sharp as in any young specimen. That these 

 animals bore by siliceous particles secreted by the foot, as suggested by 

 Mr. Hancock, has been disproved by microscopic observation ; and that 

 currents of water set in motion by vibratile cilia seemed also insuf- 

 ficient to account for the phenomenon. 



Another theory supposes that an acid is secreted by the foot, 

 capable of dissolving the rock. 



Wrightii (also from the Wenlock-shale and Limestone, Dudley), figured and de- 

 scribed by H. "Woodward in the Quart. Journ. Geol. Soc, vol. xxi., pi. xiv., figs, la 

 to \i. See also the Geol. Mag., Vol II., 1865, p. 470 (Woodcut). Can it be 

 possible that any actual relationship exists between these two remarkable and aberrant 

 forms ."— H.W. 



