EARTHS. ARGILLACEOUS. 36. Bafaltes. 127 



tunicatuii Compaa, fpontaneonfly falling into cruftofe fragments i 

 the crulls fphaerical and concentric. 

 Found with the B. columnaris; is a little fofter, with a paler 

 tinge, and crumbles more cafily. 



Wacca. Soft, fragile, compaa, a little glofTy when rubbed,- not 

 falling fpontaneonfly into fragments. 



Wacken. Kirivau, {,p. 223. 1 homjbn chenu 3./. 577. 



Wacke. SchmeiJJ. mineral 1. />. 318. 



Found in the mountains of Bohemia and Saxonyy fometimes in 

 entire ilr.ita, iometimes in thin layers under or between 

 bafalt; colour cinereous, or greenifli, or blackifh, or ycllow- 

 ifh, and often contains veins of metallic ores: lultre none, 

 frafture even, texture earthy, opake, fofr, eafily broken, and 

 feels llightly greaiy : it withers by cxpofure to the atmof- 

 phere, and then becomes more grey ; freq^uently contains 

 black mica, but never olivin^ 



TrapezHtn, Hardifh, compaa, imbibing water, growing reddiHi in the 

 air and mouldering into lamellar pieces, crackling 

 and breaking with explofion in the fire. 



Saxum impalpabile. Syst, nat. xii. 3. p. 72. n. 3. 



Corneus durus. Wall. fyst. min. i. />. 361. n. 4. 



Trap. Kirivan miner, r. p, 227. Thom/on chem, 4,/'. 1 34, 



Trapp. ScbmeiJJer mineraL I. ^. 183. 



1. Toadftone. Kir^van, \.p. 229. 



Of a dark brownifh-grey colour, abounding with cavities filled 

 with cryllallized carbonate of lime, which from the de- 

 ftru(ftion or decompofitlon of the cryllals are often empty: 

 contains filica 0,63. alumina 0,14. mild carbonate of lime 

 0,07. oxyde of iron 0,16. Withering, 



2. Rowley ragg, orTurilite. Kirnvan, i, p.zigi 



Of a black colour with numerou^s white dots, and black lamellae 

 of bafaltine, which give it a dark' brownifh-grey appearance: 

 found iti large mafles, affefting a rhomboidal form, inclofing 

 rounded pebbles of the fame fubftance : acquiring an ochry 

 CTuft by expofure to the air, and ihining internally from a 

 number of minute particles : heated in the open air it be- 

 comes magnetic, and lofes about 3 percent, of its weight: 

 it does not redden in the fire, but at 98°. melts into a po- 

 rous black mafs, partly porcehne, partly enamel : fradure 

 nearly even, fine fplintery, often inclining to the conchoi- 

 dal : contain* filica 475. alumina 3.25. oxyde of iron 200, 

 Withering, 



3. Whin-ftone, Kirivan miner, i. p. 230. 



Of a blue or greyifh-black colour, and rather hard: found in 

 detached fragments, or forming dykes in mines. 



Found in the mountains of Britain, Scandina^viat Sn/jitxerland 



