226 PEOE. S. H. EETIS^OLDS OX THE LITIIOLOGICAL [vol. Ixxvil, 



exposure in the railway-cutting before the Great Quarry is entered. 

 This band (PL XIII) is marked as ^ Liiliostrotioii Band' by 

 Vanghan in pi. v of his Avon paper. The upper limit of S^ 

 is taken at the outcrop of the lowest ^ Seminula pisolite-band. 

 Lithologically the S, rocks form one of the most varied and in- 

 teresting horizons in the "whole section, and were clearly (like the 

 underlying Upper C^ Beds) formed under ' lagoon -phase ' condi- 

 tions. Many bands are partly and some completely dolomitized. 

 For purposes oi^ description the rocks may be divided into two 

 sections: a lower section, S^ («), predominantly consisting of calcite- 

 mud stones, and an upper, S^ {h), mainly composed of dolomitized 

 Litliost ration limestone. 



S^ (a). (Thickness = about 92 feet.) — This section includes the 

 rocks below the ' back slope.' ^ The lowest beds are calcite- 

 mudstones, with several nodular algal layers. The succeeding 

 rocks are ehletiy dark-grey (or nearly black) ' china-stones.' As 

 was noted by Vaughan, while the freshly-broken surface usually 

 is dark, thej' tend to weather very white. Some of them are 

 finely banded and of the type of the ' calcaire zonaire ' of Dr. H. 

 de Dorlodot ; Avhile the surface of certain layers rises into rounded 

 elevations (PI. IX, fig. 1), which sections show to consist largely 

 of Spongiostroma. These rounded masses, sometimes 3| inches 

 in diameter, recall a similar structure in the Heminula-gregaria 

 Beds of Fawcett Mills, Kavenstonedale. Seminnla bands are 

 associated with the china-stones, many of which contain S])ongio- 

 sfpoma, others ostracods or foraminifera. Several of the shaly 

 partings are covered with what are presumably worm-castings, 

 and some of the china-stones contain peculiar vermiform bodies 

 which are probabl}^ w^orm-tubes (PL IX, fig, 2). Sections show 

 these 'tubes' to be occupied by loosely-compacted, rounded patches 

 of structureless limestone of the type described above, wdiile the 

 bulk of the rock is formed of the same material closely compacted. 

 There is one marked, but discontinuous, band of Semimcla Pisolite. 

 At several levels in lower S^ there are desiccation-breccias, and 

 Mr. E. E. L. Dixon recoo'nized desiccation-cracks in certain of the 

 china-stones. As has been already mentioned, a rock-type very 

 prevalent in the calcite-mudstones of S^ is that described above 

 (p. 225) and compared wath the structure described by Drew from 

 Florida Keys. An example from S^ is shown in PL X, fig. 4. 



Between the china-stone level and the ' back-slope ' are some 

 31 feet of strata, consisting of rather thickly-bedded and con- 

 siderably dolomitized limestone, alternating in the lower part with 

 prominent bands of black shale. These beds are exposed in the 

 slope behind the miniature rifle-range. The most conspicuous 

 shale-band, which is about 3 feet thick and contains abundant 



' The lowest, that is, with the exception of the discontinuous band 

 mentioned in the next paragraph as occurring in S^(a). 



2 The ' front slope ' and ' back slope ' (PI. XIII) are two prominent bedding- 

 planes, thus denominated by Vaughan in his Avon paper, p. 113, and used as 

 datum-lines. 



