HARDWICKE'S SCIENCE-GOSSIP. 



6i 



of darker-coloured calcareous shales. Mineralogically 

 considered the rock is sub-crystalline, with an irregular 

 or amorphous cleavage, and not unfrequently exhibits 

 a splintery fracture, while its general hardness may 

 be taken at 2"8 and its specific gravity at 2' 5. It 

 tlVervesces rapidly in acid, is almost infusible before 

 the blowpipe at an ordinary heat, though it parts with 

 its carbonic acid very readily, shines with a vivid 

 brightness, and ultimately becomes quicklime. The 

 following may be accepted as a rough analysis of the 

 limestone proper. 



Carbonic acid 42*0 



Lime 48 'o 



Magnesia 2'o 



Alumina 2"o 



SiHca 3*5 



Various (sulphur, oxide of iron, &c.) 2'5 



lOO'O 



The rock generally has the appearance of being 

 built up or composed of Entrochi (wheelstones) or 



Fig. 37.— Stem of 

 Entrochi. 



Fig. 38.— Stem of Platyori- 

 nns la-vis (nat. size). 



Fig. 3<3.— Plate of Archieoci- 

 dan's nrii (nat. size). 



Fig. 40. — Joint of Encrinite 

 ("St. Cuthbert's Bead") 

 (nat. size). 



remains of Encrinites, a variety of Crinoid wonder- 

 fully numerous in this formation. These marine 

 animals closely resembled plants, hence the name 

 " stone lilies," and, like plants, were fixed to one spot. 

 They consisted of innumerable articulating joints 

 placed one above another upon a base or root attached 

 to the sea-bottom. This stem, often several feet in 

 length, was surmounted by a cup-shaped arrangement 

 (pelvis) containing the body of the animal, from which 

 issued long jointed tentacula or fingers, capable of 

 being extended horizontally for the purpose of allow- 

 ing it to catch its prey. Not unfrequently the stems 

 consisted, as in the species Moniliformis, of several 

 thousand Entrochi or joints, and through the whole 

 series ran an alimentary canal connecting the base 

 with the stomach. The holes in the.joints caused by 

 the existence of this canal suggested to the former 



inhabitants of some limestone districts the idea of 

 their having at one time been beads, and indeed they 

 have often been used as such. It is to these that Sir 

 Walter Scott alludes in " Marmion." 



"On a rock by Lindisfarn, 

 St. Cuthbert sits and toils to frame 

 The sea-born beads that bear his name." 



Myriads of these Encrinite stems and joints, the 

 latter varying in diameter from a Hne to an inch, are 

 crowded into the limestone of Invertiel and other 

 places, though the most perfect examples are those 

 found in the looser calcareous shale. The Encrinite is 

 never found entire at this and adjoining quarries, but 

 bases and parts of the pelvis and tentacula are by 

 no means rare. Other characteristic fossils found 

 here include, Cyathocriims planus, C. tiibercnlatus^ 



Fig. 41. — Stem of Potcriocrinus crassns. (From Taylor's 

 ("Common British Fossils.") 



C. riigosus, Platycrimis Iczvis, Foieriocrtjms iennisy 

 Cyathophyllum turbinatuiii. Plates of Af'chiBocidaris 

 tirii, Faiestella mcmbranacea, Prodiutits longispinus^ 

 P. semiretictdaUis, Spirifera lincata, S. glabra, S, 

 trigonalis, Orthis Mitchiliiii. 



The plates of the Archteocidaris are usually found 

 singly in the looser shale, and are highly interesting 

 as being the remains of one of the very earliest forms 

 of the family Cidaris {Echinodermata). These will 

 probably be far better understood by breaking in 

 pieces and comparing the separate sections or plates 



