S38] 



FARMERS' REGISTER. 



626 



Fourth, serpentine, which isconstiluled by Ibkl- 

 -par and a body named resplendent hornblende; 

 and their separate crystals arc often so small as to 

 irive the stone a nnilbrm apjiearance: this rocl( 

 abounds in veins of a substance called steatite, or 

 soap rock. 



Fifih, porphyry, which consists of crj^stais of 

 feldspar, embedded in the same material; buf. usu- 

 ally of a dill'erent color. 



Sixth, s;ranular marble^ which consists entirely 

 of crystals of carbonate of lime; and which, when 

 its color is while, and texture fine, is the sub- 

 stance used by statuaries. 



Seventh, chlorite schist, which consists of chlo- 

 rite, a green or <rray substance, somewhat analo- 

 gous to mica and feldspar. 



Eighth, qnartzose rock, which is composed of 

 quartz in a jxranuiar form, sometimes united to 

 small quantities of the crystalline elements, which 

 liave been mentioned as belonging to the other 

 rocks. 



The secondary rocks are more numerous than 

 the primary; but twelve varieties include all that 

 ;ire usually found in these islands. 



First, grmnvacke, which consists of fragments 

 of quartz, or chlorite schist, embedded in a ce- 

 ment, principally composed of fJ^Jiispar. 



Second, siliceous sandstone, which is composed 

 of fine quartz or sand, united by a siliceous ce- 

 ment. 



Third, limestone, consisting of carbonate of 

 lime, more compact in its texture than in the gra- 

 nular marble; and often abounding in marine 

 exuvife. 



P^ourth, aluminous schist or shale, consisting of 

 the decomposed materials of difl'erent rocks ce- 

 mented by a small quantity of ferruginous or sili- 

 ceous matter; and olten containing the impres- 

 sions of vegetables. 



Fifih, calcareous sandstone, which is calcareous 

 sand, cemented by calcareous matter. 



Sixth, ironstone, lormed of nearly the same 

 materials as aluminous schist or shale; but con- 

 taining a much larger quantity of oxide of iron. 



Seventh, basalt or ivhinstone, which consists of 

 feldspar and hornblende, with materials derived 

 from the decomposition of the primary rocks ; the 

 crystals are generally so small as to give the rock a 

 homogeneous appearance ; and it is often disposed 

 in very regular columns, having usually five or six 

 sides. 



Eighth, bituminous or common coal. 



Ninth, gypsum, the substance so well known by 

 that name, which consists of sulphate of lime; and 

 often contains sand. 



Tenth, rock salt. 



Eleventh, chalk, which usually abounds in re- 

 mains of marine animals, and contains horizontal 

 layers of flints. 



Twe\f\h, plumb pudding stone, consistinjrof peb- 

 bles cemented by a ferruginous or siliceous ce- 

 ment. 



To describe more particularly the constituent 

 parts of the different rocks and strata will be 

 unnecessary; at any time, indeed, details on this 

 subject are useless, unless the specimens are exa- 

 mined by the eye ; and a close inspection and 

 comparison of the difierent species will in a short 

 time enable the most common observer to distin- 

 guish them. 



The highest mountains in these islands, and in- 

 Vol. VI.— 79 



deed in the whole of the old continent, are consti- 

 tuted by granite; and this rock has likewise been 

 lljund at tlic greatest depths to which the industry 

 of man has yet been able to penetrate ; micaceous 

 schist is olten Ibund immediately upon granite; 

 serpentine or marble upon micaceous schist ; but 

 the order in which the primary rocks are grouped 

 together is various. Marble and serpentine are 

 usually fijund uppermost ; but granite, though it 

 seems to form the foundation of the rocky strata of 

 the globe, is yet sometimes discovered above mica- 

 ceous schist. 



The secondary rocks are always incumbent on 

 the primary; the lowest of them is usually grau- 

 wacke; upon this limestone or sandstone is often 

 Ibund; coal generally occurs betAveen sandstone 

 or shale ; basalt often exists above sandstone and 

 limestone; rock salt almost always occurs asso- 

 ciated with red sandstone and gypsum. Coal, ba- 

 salt, sandstone, and limestone, are ofien arranged 

 in different alternate layers, of no considerable 

 thickness, so as to form a great extent of country. 

 In a depth of less than 500 yards, 80 of these dif- 

 ferent alternate strata have been counted. 



The veins which afford metallic substances, are 

 fissures vertical or more or less inclined, filled with 

 a material different fiom the rock in which they 

 exist. This material is almost always crystalline; 

 and usually consists of calcareous fluor spar, 

 quartz, or heavy spar, either separate or together. 

 The metallic substances are generally dispersed 

 through, or confusedly mixed with these crystal- 

 fine bodies. The veins in hard granite seldom af- 

 ford much useful metal; but in the veins in soft 

 granite and in gneiss tin, copper, and lead are found. 

 Copper and iron are the only metals usually found 

 in the veins in serpentine. Micaceous schist, sienite, 

 and granular marble are seldom metalliferous 

 rocks. Lead, tin, copper, iron, and many other 

 metals, are found in the veins in chlorite schist. 

 Grauwacke, when it contains few fragments, and 

 exists in large masses, is often a metalliferous 

 rock. The precious metals, likewise iron, lead, 

 and antimony, are (bund in it : and sometimes it 

 contains veins, or masses of stone coal, or coal 

 fi-ee from bitumen. Limestone is the great me- 

 talliferous rock of the secondary family ; and lead 

 and copper are the metals most usually found in 

 it. No metallic veins have ever been found in 

 shale, chalk, or calcareous sandstone; and they 

 are very rare in basalt and siliceous sandstone.* 



Incases where veins in rocks are exposed to the 

 atmosphere, indications of the metals they contain 

 may be ofien gained from their superficial appear- 

 ance. Whenever fluor spar is (bund in a vein, 

 there is always strong reason to suspect that it is 

 associated with metallic substances. A brown 

 powder at the surface of a vein always indicates 

 iron, and often tin ; a pale yellow powder lead ; 



* Fig. 16. will give a general idea of the appearance 

 and arraijgement of rocks and veins. 



Explanation of Figure 16. 



1 Granite. — 2 Gneiss. — 3 Micaceous Schistus. — 4 

 Sienite. — 5 Serpentine. — 6 Porphyry. — 7 Granular 

 Marble. — 8 Chlorite Schist. — 9 Quartzose Rock. — 10 

 Grauwacke.— 11 Siliceous Sandstone.— 12 Limestone. 

 — 13 Shale. — 14 Calcareous Sandstone. — 15 Iron Stone. 

 — 16 Basalt— 17 Coal. —IS Gypsum.— 19 Rock Salt.— 

 20 Chalk.— 21 Plnra Pudding Stone— AA Primary 

 Mountains. — BB Srcondary Mountains. — aaa Veins. 



