344 SERBIAN. 



sediment forming the clays in which the 

 septaria are found,frequentiy collecting round 

 shells, plants, or other organic substances. 

 In the contraction undergone by these con- 

 cretions during the process of solidification, 

 they became traversed by cracks, which in 

 many cases have subsequently become filled 

 with an infiltration of carbonate of lime or 

 Calc-spar, and it is from these septa, or 

 divisions, that the concretions have derived 

 their name of Septaria. The cracks gene- 

 rally form regular figures, all more or less 

 partaking of a pentagonal shape, and the 

 tendency of clayey matter to assume such 

 figures in the contraction consequent on 

 drying, may be observed on the surface of 

 the mud of any shallow pool or puddle from 

 which the water has dried off. 



In consequence of the regularity of the 

 patterns produced by the septa, Septaria are 

 sometimes called " Turtle- stones,''^ from their 

 fancied resemblance to the plates forming 

 the shell of a tortoise or turtle, the fossil 

 remains of which they have been sometimes 

 supposed to be by the ignorant. The turtle- 

 stones from the Oxford Clay, of the neigh- 

 bourhood of Weymouth, when cut and 

 polished, form very handsome circular slabs 

 for tables, examples of which may be seen in 

 the entrance hall of the Museum of Practical 

 Geology. (A 22, A 25.) 



Septaria, when burned and ground, afford 

 the best kind of Roman cement, and are in 

 great request for that purpose. They are 

 chiefly procured by dredging off the coasts 

 of Essex, Hampshire, and Sussex, where 

 they have accumulated at the bottom of the 

 sea, after the softer materials forming the 

 mainland have, by its destruction, been 

 carried away. The septaria obtained from 

 Harwich and Essex, as well as those from 

 Chichester Harbour, on the coast of Sussex, 

 have been derived from the London clay, 

 while those found in Christchurch Bay be- 

 long to the Barton clay formation. 



M. P. G. Table-case vi. in Hall : from 

 Oxfoi'd clay, Upper Gallery, AVall-case 44. 



Fig. 383. 



Serbian, Breithaupt. See jMilosciiine. 

 The name is derived from that of the locality 

 {Serbia) in which it is found. 



SERPENTINE. 



Sericite, K. List. A variety of Mar« 

 garodite, allied to Damourite, occurring in 

 undulating foliations. Colour greenish or 

 yellowish-white, with a silky lustre. Found 

 at Nerothal. near Wiesbaden, in slate, with 

 Quartz and Albite. H. 1. S.G. 2-89. 



Serikolite. See Satin Srae. 



Serpentine, Jameson, Haiiy, Phillips^ 

 Werner. Usually occurs massive, granu- 

 lar, fibrous, or foliated ; also as pseudomor- 

 phous crystals after Chrysolite, Augite, &c. 

 Colour chiefly green ; ieek-green passing 

 into greenish-black and blackish- green, 

 sometimes oil- and olive-green, or yellow, 

 rarely yellowish-brown. The colour is sel- 

 dom uniform, but generally consists of 

 several tints, arranged in dotted, striped, 

 and clouded delineations. Faintly trans- 

 lucent at the edges to opaque. Lustre dull, 

 or faintly glimmering. Streak white. Sec- 

 tile. Tough. Fracture splintery, or con- 

 choidal. Slightly unctuous to the touch. 

 H. 3 to 4. S.G. 2-5 to 2-6. 



Comp. Hydrated silicate of magnesia, or 



Mg9 bi^ H6 = magnesia 43'35, silica 43*64, 



water 13-01 = 100. 

 Aiialysis, from Ballinahinch in Galway : 



Silica 40-12 



Magnesia . . . .40-04 

 Alumina .... 2-00 

 Protoxide of iron . . S-47 

 Water .... 13-36 



98-99 



BB on charcoal, fuses with difficulty at 

 the edges : with borax dissolves readily, 

 usually giving an iron reaction. 



Soluble in muriatic and sulphuric acids. 



Localities. — English. Kynance Cove,Goon- 

 hilly Downs, Cadgwith, and other places in 

 the Lizard district. Anglesea; Pary's mine 

 and Bullock's quarry. — Scotch. Alie Hills, 

 Aberdeenshire. Portsoy, in Banffshire, Kil- 

 lin, Perthshire (fibrous). Swinaness, in the 

 Shetlands. — Irish. Ballynahinch quarries, 

 CO. Galway. Co. Wicklow, near Westport, 

 Co. Mayo. — Foreign. Zoblitz, in Upper 

 Saxony. Bohemia. Silesia. Corsica. Italy. 

 Siberia. Canada, at Gaspe Mount, &c. 



Name. From its fancied resemblance to 

 the markings on the skin of a serpent. 



Serpentine has been divided into Precious 

 or Noble Serpentine, comprising the purer 

 translucent and massive varieties, with a 

 rich oil-green colour. 2nd, Common Ser- 

 pentine, or the opaque varieties forming ex- 

 tensive rock masses like those of the Lizard, 

 Portsoy, Anglesea, and Zoblitz. 3rd, Fibrous 



