Vol. 57.] PEITDLESIDE GROUP AT PENDLE HILL, ETC. 395 



J^o. 226, which is the well-known Black Marble of Ashford (Derby- 

 shire), from the Mountain Limestone Series, we find only a trace of 

 iron and only 1-07 per cent, of organic matter. The black marble 

 is a dark-grey, compact rock, weathering pale grey, but when 

 polished, quite black. 



From almost every part of the area described in this paper the 

 limestones in the shales are of this black type alone ; sometimes 

 occurring as layers of black hard nodules, bullions, lying in the 

 soft black shale, or as indurated portions of the shale itself, with a 

 tendency to break up into shaly material on exposure to the 

 weather; but on Pendle Hill itself, as we have already shown, rocks 

 of various other types occur in addition to the black limestone ; of 

 these Nos. 316 & 319 are a fair illustration. No. 316 is the rock 

 which assumes ' anvil '-forms on weathering, and No. 319 is the 

 sponge-bearing rock described on p. 397. It will be seen that they 

 are limestones with a fairly high percentage of silica. 



None of the Pendleside rocks analysed show any appreciable 

 amount of magnesia, but some of the beds, evidently the product of 

 alteration of the above-mentioned limestones, are almost pure 

 dolomites, and sections show the passage of one form into the 

 other. 



In the grey limestones, such as No. 316, chert appears in small 

 patches, but beds of chert also occur from | inch to 18 inches thick 

 at intervals among the limestone. There are two varieties, one 

 black, homogeneous, and compact, and another grey and more 

 porous in appearance. 



One of the black, rather concretionary limestones from near the 

 top of the limestone series on Pendle HiU, at the upper limit of the 

 wuod above Little Mearley Hall, weathers on the surface, possibly 

 through the action of peaty water, into a layer of chocolate-brown 

 soft material with a weakly developed cone-in-cone structure^ 

 appearing as small concentric circular depressions measuring about '25 

 to "5 inch in diameter. We have not obtained enough of this material 

 for analysis, but on treatment with cold hydrochloric acid it readily 

 breaks down, without effervescence, into a dark-brown syrup with 

 an abundant residue of minute crystalline rods of silica, generally 

 with flat terminations. These rods are about 1*4 mm. in length 

 and from '3 to 0*4 mm. broad; they are probably broken sponge- 

 spicules. The material is evidently a kind of rotten stone. 



Nos. 227 & 187 are typical examples of the white limestone 

 of HiU Bolton, Thorpe (near Grassington), and Bunster Hill, 

 Dovedale, on the Staffordshire side of the river. We have analysed 

 these samples, in order to show the very noteworthy difference 

 in purity between the white limestone of the Mountain Lime- 

 stone and even the purest in the Pendleside Group. 



We desire particularly to contrast the analysis of No. 227 from^ 



Hill Bolton, one of the ' knoll-reefs ' described by Mr. Tiddeman ^ 



with that of No. 346, which we understand, according to Mr. Tidde- 



man's view, to be a portion of the same rock which had rolled down 



1 Brit. Assoc. Eep. 1889 (Newcastle) p. 602. 



a J. G. S. No.227. ^B 



k 



