HEAT — METAMORPHISM. 309 



eruption. The hot waters are in constant ebullition and have their intermittent jets. Be- 

 sides escaping steam, there is some carbonic acid given out, and siliceous deposits are 

 made from the hot waters. Geysers occur also on the island of Celebes, in the volcanic 

 region on its northeastern extremity in the district of Manado. 



IV. METAMORPHISM. 



Metamorphism signifies change : not merely change in form, as might 

 be inferred from the composition of the word, but also, like the correspond- 

 ing word metamorphosis, change in nature or constitution. In geology, it is 

 change in texture, crystalline structure, or mineral constitution ; as when a 

 common limestone becomes crystallized, and thereby converted into statuary 

 marble, or a sandstone into gneiss or granite, or an augitic rock into a horn- 

 blende rock, or a massive rock into a laminated or foliated kind. 



The terms metamorphic and metamorphism were proposed by Lyell in 

 the first edition of his Principles of Geology (1831-1833) with reference to 

 altered rocks of both local and regional extent. 



In Vol. III. he says, on page 372: "It appears from sections described 

 by Hugi, that some of the secondary beds of limestone and slate, which are 

 overlaid by granite, have been altered into gneiss and mica schist. These 

 altered sedimentary formations are supposed by M. Elie de Beaumont to be 

 of the age of the Lias of England, and others to be even as modern as the 

 Jurassic or Oolytic formations." On page 373 he says : " According to 

 these views, gneiss and mica schist may be nothing more than micaceous and 

 argillaceous sandstones altered by heat, and certainly in their mode of strati- 

 fication and lamination, they correspond most exactly." 



" Granular quartz may have been derived from siliceous sandstone ; clay 

 slate may be altered shale, and shale appears to be clay which has been 

 subjected to great pressure." " Granular marble has originated in the form 

 of ordinary marble, having in many instances been replete with shells and 

 corals now obliterated." In the edition of 1842, he speaks of fossiliferous 

 formations, some of them of the age of the Silurian strata, as near Christiania 

 in ISTorway, others belonging to the Oolytic period, as around Carrara in 

 Italy, which had been converted partially into gneiss and mica schist and 

 statuary marble. Among local changes he mentions the case of the basalt 

 dike in Anglesea, 134 feet wide, cutting through strata of shale and limestone 

 which were altered for 30 feet from the dike, " having the shale in several 

 places converted into hard-porcelanous jasper, in the hardest parts of which 

 the fossil shells, principally Productoe, were nearly obliterated " ; " and the 

 argillaceous limestone had lost its earthy texture and become granular 

 and crystalline." Through investigation since, such facts, both of regional 

 and local origin, have been greatly multiplied. 



The Taconic region, on the borders of New York and New England, 

 affords a good illustration. The rocks are least crystalline in the northern 

 and the western parts of the region, and consequently fossils were to be 

 looked for in those parts. They have been found in Vermont down to 



