1873.] LUCAS — ORIGIN OE CLAY-TRONSTONE. 363 



He considered that they were connected with the disturbances 

 which have taken place in comparatively recent times along the 

 eastern coast of the Morea. The sulphur, which usually occurs in 

 small globular masses in gypseous beds, was found in these Solfa- 

 taras in a crystalline form, and in connexion with the fissures from 

 which the heated gas issues. There was therefore a marked differ- 

 ence in the manner of its occurrence, both in Italy and in Greece. In 

 Greece the sulphur- deposit in nodules is found on the west of the 

 principal chain of mountains, and the crystalline sulphur on the east. 

 In Italy the crystalline sulphur is limited to the vicinity of Vesuvius, 

 and the nodules are abundant both in Sicily and on the east coast 

 of the mainland. 



3. On the Origin of Clay- Ironstone. By J. Lucas, Esq., F.G.S., 

 of the Geological Survey of England. 



A. i. Clay-ironstone* is an impure carbonate of iron, containing 

 generally from 30 to 33 per cent, of metallic iron mingled with 

 varying proportions of clay, oxide of manganese, lime, and magnesia. 



2. "When the principal foreign matter in this mineral is of a 

 bituminous or combustible nature the variety thus formed is called 

 "Black band"f. This combustible matter often amounts to 25 or 

 30 per cent. 



3. Sometimes lime so far predominates in Clay-ironstone as to 

 give it the general appearance of a compact limestone, when the 

 presence of iron may be detected by the great weight of the mass, 

 and by the decomposition of the exterior, which turns a dark brown 

 to the depth of a quarter of an inch or more on oxidation. 



4. Through the intermediate forms it passes into a pure lime- 

 stone. Such limestone bands are characterized by being densely 

 compact, very hard, dark-coloured, and by being devoid of organic 

 remains. 



B. 1. The foregoing varieties occur throughout the vast thickness 

 of delta-deposits whose remains now constitute the Carboniferous 

 formations. They lie in beds varying in thickness from a fraction 

 of an inch to about 2 feet. 



2. When the top of a bed is exposed it is often found to be tra- 

 versed by a series of cracks, which present the general appearance 

 of a net of very unequal and irregular mesh. These cracks are 

 filled with sediment like that in which the bed of Clay-ironstone 

 lies. 



3. Yery frequently the beds of all varieties are so irregular as to 

 appear in clean section like a layer of flattened nodules. These 

 irregular layers are always very thin. 



4. A glance over the copious details contained in Jukes's " Me- 



* Miller's ' Elements of Chemistry,' pt. ii. p. 575, ed. 1864 ; ' Elements of Geo- 

 logy,' p. 492, 6tH ed. ; Student's Elements, p. 385 ; Bristow's ' Glossary of 

 Mineralogy,' p. 87; ' Manual of Geology,' Jukes, p. 356, ed. 1862. 



t Miller's ' Elements,' pt. ii. p. 575, ed. 1864 ; ' Glossary of Mineralogy,' 

 Bristow, p. 44. 



