Vol. 57.] PENDLESIDE GEO UP AT PENDLE HILL, ETC. 397 



calcite longer than the other forms. Crinoid-fragraents have seldom 

 retained their original outline ; in places the original calcite-cleavage 

 remains, but more often this has been destroyed, and the only in- 

 dication is the minute structure outlined in opaque grey material 

 or in pyrites. Silicification on a small scale has taken place, in the 

 form of irregular patches in the interior of crinoid-fragments. 



Dolomitization may be traced from a few scattered rhombs and 

 groups of crystals in a fairly pure limestone, through all gradations 

 to a rock like the one from the old quarry in the wood above Little 

 Mearley Hall, in which the process is complete and a true dolomite is 

 formed, all indications of organic structure having been removed and 

 only a thin dark line remaining to mark the boundary of theparticles, 

 and even this is often absent. Where the single rhombs are formed 

 in the limestone they seem, as a rule, to commence on the margin of 

 the organic body and grow towards its interior, entirely obliterating 

 all structural details. It may be noted here that, where crystalline 

 calcite has trespassed from the matrix into an organism, it is more 

 common to find a trace of the original outline than when dolomite- 

 crystals have behaved in the .same way. 



In the finer-grained beds, noticeably those with the ' anvil '-forms, 

 the organic remains are less easily identified , and calcifiedsponge- 

 spicules take a more prominent part. These spicules are mostly in 

 the condition of clear calcite, with dark grey indistinct outlines. 

 One of these sponge-bearing limestones, a compact, dark-grey to 

 brown rook (No. 319), presents a very striking appearance, on account 

 of the presence of small sponges, little patches g to | inch in 

 diameter distributed over the lamination-planes (the lamination is 

 probably determined by the sponges). The sponges are themselves 

 in a siliceous condition, and as they appear whitish or yellow on 

 the dark rock, they are fairly conspicuous. On treating lumps of 

 this rock with cold hydrochloric acid an abundant residue of spicules 

 and small silicified organisms remains. In the slide, however, 

 this rock does not materially differ from the ordinary fine-grained 

 limestone. 



Cherts. 



Associated with the limestones are two varieties of chert : one is 

 a pale light-grey rock, weathering white ; the other is black and 

 compact, without any sign of organisms in the hand-specimen, but 

 when sliced is seen to be a mass of ill-defined sponge-material. 

 The two forms occur repeatedly in the upper part of the exposure 

 sometimes in the grey limestone and sometimes in the brown 

 dolomitic beds. 



The first-mentioned variety is undoubtedly a silicified representa- 

 tive of the grey limestones, and like them is found in several grades 

 of texture. The coarse-grained chert is unlike any of the cherts that 

 we have hitherto examined from the Mountain Limestone Series ; 

 it is extremely hard and breaks into cuboidal pieces. The organisms 

 already mentioned as occurring in the grey limestones are easily 

 distinguishable by the unaided eye. Examination of the weathered 



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