HA R D WICKE'S S CIENCE- G O SSI P. 



253 



away, leaving only thin plates of flinty material, such 

 as was deposited between the joints, so arranged 

 around the filled-up hollow, or alimentary canal which 

 ran down the whole length of the stem, as to give the 

 appearance of the screwed end of a bolt. For mile 

 after mile, the geologist may walk along the Derby- 

 shire mountain roads, and find the stone walls on either 

 hand composed of nothing else but Encrinital remains. 

 Sometimes the rock containing them is very hard, and 

 then it will be worked as marble, which, when polished, 



splendid relief from the jet-black stone in which 

 they are imbedded. The stones of the mountain 

 roads are usually picked off the surface, where 

 the limestone rocks have been most weathered. 

 And, as the structure of most fossils imbedded in 

 limestones is such that they are harder than the 

 limestone itself, it follows that when surface weather- 

 ing has gone on for some time, the fossils will 

 stand out in relief. Millions of Encrinite stems may 

 be found thus dispersed over the surfaces of the 



Fig. 196. Woodocriints macrodaciylus. 



will be used for mantel-pieces. Many of my readers 

 must be acquainted with this polished grey marble, 

 full of all sorts of objects, but especially of these 

 Encrinite stems, cut 

 across, lengthwise, or 

 at all kinds of angles, 

 so that the appear- 

 ance varies with each 

 individual fossil. 

 When the limy matrix 

 is quite black (as it is 

 at Ashford,near Bake- 

 well), the marble is all 

 the more valuable for 

 economic purposes, 

 for then the white 

 fossils stand out in Fig. 197. Head of Poteriocrhms. 



Fi^. 198. Stem of Encrinite, most abundant in Carb. Lime- 

 stone {Potcriocrinns crassus). 



Carboniferous limestone whose fragments are used 

 for wall-building. In Clithero, Lancashire, at a small 

 elevation known as Salt Hill, the rock is also built up 

 of Encrinite stems. In this case, however, the fossils 

 are loose and incoherent, stems and ossicles lying 

 together almost uncemented by any matrix, or by one 

 which speedily weathers and liberates the fossils. The 

 consequence is that joints and short stems of Encrinites 

 are so loose and abundant, that they are procured as a 

 kind of limy gravel to mend or make garden paths 

 with ! 



Some of these abundant]. Encrinite stems in Derby- 

 shire are often more than one inch in diameter. This 

 species, known as Potcriocrir.iis crassits, was by far the 

 most wide-spread and abundant of all the Carboni- 

 ferous Crinoids. The head, or body of the Encrinite, 

 was tapering, and in this respect it resembled the 



