ROCK. 



alJy : it also sometimes contains horn- 

 blende, actyrtblite, asbestos, serpentine, 

 talc, steatite, tremolite, garnet, calcare- 

 ous spar, and slate-spar. 6. Primitive 

 trap, is a mountain which seems intimate- 

 ly connected with clay-slate. The term 

 trap had been long used without a defi- 

 nite signification ; but Werner has re- 

 sricted its application to rocks, principal- 

 ly containing hornblende, and black iron- 

 clay ; the iron-clay first appearing in the 

 transition, and increasing in rocks of the 

 newer periods. There are three distinct 

 species of primitive trap. Common horn- 

 blende rock, under which are comprised, 

 hornblende rock, and horneblende slate. 

 Hornblende with felspar, a subordinate 

 kind of which is greenstone, which has 

 the following varieties : common green- 

 stone, a granular aggregate of hornblende 

 and felspar. Porphyritic greenstone is 

 the former, containing crystals of felspar. 

 Greenstone porphyry, is the black por- 

 phyry of the ancients; crystals of felspar 

 are here also included, but the granular 

 structure of the basis is hardly discover- 

 able. Green porphyry, in which the gra- 

 nular structure is no longer visible, and 

 crystals cf compact felspar are included. 

 The second species of primitive trap is 

 greenstone slate, composed of horn- 

 blende and compact felspar, arranged in 

 a slaty structure ; and the third is an inti- 

 mate mixture of hornblende with felspar, 

 including mica in scales. It is found in 

 beds in gneiss and mica-slate. 7. Ser- 

 pentine is a simple mountain rock, indis- 

 tinctly stratified. A great variety of other 

 mineral bodies are found in it, and it is 

 sometimes indeterminately mixed with 

 limestone, forming what is termed verde 

 antico. 8. Porphyry is a compound rock, 

 formed of one substance in the form of 

 grains or crystals, imbedded in another 

 as its basis. The base is clay -stone, horn- 

 stone, compact felspar, pitch-stone, pearl- 

 stone, or obsidian : the imbedded crystals 

 are of quartz or felspar. There appears 

 to be two formations of porphyry ; the 

 oldest consists principally of hornstone 

 and felspar porphyry ; and the newer of 

 clay, pitchstone, pearl-stone, and obsidian 

 porphyry. 9. Sienite is a compound, 

 granular, aggregated rock, formed of fel- 

 spar and hornblende, and sometimes con- 

 taining quartz and black mica. The horn- 

 blende distinguishes this rock from gra- 

 nite ; but the felspar, which is almost al- 

 ways red, and seldom inclining to green, 

 is the most abundant and essential por- 

 tion of the rock ; a circumstance which 

 distinguishes it from greenstone, in which 

 VOL. V, 



the felspar predominates, and is of a 

 greenish colour ; whilst in sienite it is red 

 or reddish. 10. Topaz rock is composed 

 of quartz, topaz schorl, and a small por- 

 tion of lithomarge : the stratification of 

 this rock is uncommonly distinct. 11. 

 Quartz rock is a simple mountain rock, 

 composed of small and flattish granular 

 distinct concretions. This, as well as the 

 former rock, is not very frequently met 

 with, nor is of considerable extent. 12. 

 Primitive flinty-slate is a simple rock, of 

 which there exist two subspecies ; com- 

 mon flinty slate, and Lydian stone. It is 

 met with in considerable beds in clay- 

 slate. 13. Primitive gypsum is a simple 

 rock, which is distinguishable from the 

 newer gypsum, by its being mixed with 

 mica and clay-slate. 14. White stone is 

 a rock, which is sometimes of a slaty, and 

 sometimes of a granular structure, and is 

 chiefly composed of compact felspar, 

 with a small proportion of mica. 



Whilst the primitive mountains were 

 still covered with water, it is supposed 

 that a considerable rising of the waters 

 took place, from which were deposited 

 rocks of porphyry, sienite and pitch-stone. 

 These contain very little mechanical de- 

 position, no petrifactions, and little or no 

 carbonaceous matter. These rocks are 

 considered as the second porphyry and 

 sienite formations. 



The rocks which are considered as 

 transition rocks are, 1. Transition lime- 

 stone, differing from the primitive in its 

 variety of colours, and by its containing 

 the remains of marine animals ; and from 

 the floetz in its minute granular structure 

 giving a splintery or flat conchoidal frac- 

 ture. 2. Transition trap ; under which 

 species we have transition green stone, 

 distinguished by being less crystalline 

 than the primitive, and more so than the 

 floe"tz ; and transition amygdaloid. 3. 

 Grey wacke", which is more abundant 

 than the two preceding, und also marks a 

 particular period in the formation of 

 rocks, it possessing the appearance of me- 

 chanical deposition. There are two 

 kinds, grey wacke and grey wacke slate : 

 the former is a sand-stone, differing from, 

 those of later formation, in being compos- 

 ed of portions of sand of larger size in 

 grey coloured clay-slate ; the latter ob- 

 tains its slaty structure, in a great mea- 

 sure, from the smallness of the sandy par- 

 ticles. This rock is extremely abundant 

 in metals, and is very generally distribut- 

 ed. 4. Transition flinty-slate. 5. Tran- 

 sition gypsum. The two latter do not 



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