^{page 517 note 1} In the discussion which followed, Prof. Ansted referred to swallow-holes occurring in granite in Sark and Cephalonia. Enlarged fissures and pits, which receive streams, are, doubtless, to be met with in strata of all sorts, but swallow-holes of the first class described in the paper, whose characteristic features are vertical sides, fluted surfaces, and isolated pillars, are believed by the author to be restricted to a few formations only.

^{page 517 note 2} See Prestwich's paper on swallow-holes on the Chalk hills near Canterbury. Quarterly Journal Geological Society, x. p. 222.

^{page 517 note 3} In the discussion Mr. H. Woodward cited the case of underground rivers in the Chalk beneath Norwich, which had been tapped by the deep-main sewers lately constructed, and which had proved almost insurmountable obstacles to the completion of the works. He also mentioned the case of a sudden sinking of land at Lexham, Norfolk, upon the farm of Henry Childs, Esq., leaving a deep circular depression in the field. A ploughman, plough, and pair of horses at work in the field were carried down with the land, but were providentially rescued, without harm, from a depth of twenty feet or more. Such pits, he remarked, were evidently the result of the falling in of the roof of one of these deep-flowing rivers in the Chalk beneath.

^{page 518 note 1} Prof. Phillips mentions a glen formed by a line of ancient subterranean caverns. The subsidence of the roof appears to have originally determined the direction of the watercourse. See paper on Formation of Valleys near Kirby Lonsdale, British Association Reports, 1864.

^{page 519 note 1} In the subsequent discussion, Mr. T. McK. Hughes, of the Geological Survey, gave his opinion that the strata beneath these hollows were Devonian and noncalcareous. He also supported the ice theory mentioned in the paper.