MINERALOGY. 



433 



Getgnoslic and Geographic Situations. It occurs 

 along with porphyry and claystone, in the Pentlands 

 and Ochils ; also 'in Arran, and in several places on 

 "aphiT. the east coast of Scotland, associated with old red sand- 



tualioa. Ston,'. 



Geognotu'c 



Fdpir 

 Pecpfcyrv. 



ClinktUne. 

 porphyry. 



r: ,<-t>:,. 



V jrt v . 



fitioa. 



4. Felspar Porphyry, Jameson. 

 Felspath Porphir, Werner. 



This rock diners from the preceding, in always con- 

 taming imbedded grains and crystals of felspar. 



Geognostic and Geographic Situations. It occurs along 

 with clay-stone porphyry, and other rocks of this se- 

 ries, in the Pentlands and Ochils, and in other parts 

 of Scotland. 



5. Clinkstone Porphyry, or Porphyry-slate, Jameson. 

 Klingstein Porphir, Werner. 

 Phonolith, Daubuisson. 



This rock has a basis of that kind of felspar na- 

 d clinkstone, with imbedded crystals of fel 

 whence it is named clinkstone porphyry, or 

 ry-alate, from ha slaty structure. The colour 

 basil is gi tina'sh, yellowish, smoke, bluish, or asb- 

 grey ; suuiitiames also blackish-green, and, when 

 much impregnated with iron, liver-brown and reddish, 

 brown. Sometimes several colours occur in the same 

 maw, awl it is ncoasiansfly marked with greyish-colour- 

 ed spots, and frequently shews dendritic delineations 

 on its surface. It* fracture is splintery in the small but 

 slaty in the large. Hardnese same as that of felspar. 

 It is more or lew translucent on the edges, and some 

 varieties are <>; 



Imbedded minerals. Besides the imbedded grains and 

 crystals of felspar, it also occasionally contains crystal* 

 of augite and basaltic hornblende, zeolite in drusv ca- 

 vities, and very seldom quartz, calcareous spar, iron- 

 pyrites, and iron-sand. It is amimtinms vesicular. 



' .Structure. It is frequently arranged in columns and 

 tables, like those of basalt. 



Decomposition. It long resists the action of the wea- 

 ther, but in course of time it becomes covered with a 

 thin crust, which has usually a greyixh-white colour in 

 the pure, but of a reddish colour in the iron-shot 



Farmsf Like basalt, it frequently forms conical and 

 tabular bills, aad exhibits numerous, striking, and rug. 

 ged cuffs. 



Geognostic Situation. ll occurs in imbedded msisei. 

 msHlen. beds, and veins, in red sandstone, in the coal-formation, 



and also in secondary limestone. 



graphic Geographic Situation It is a frequent rock in the 

 islands or Arran and Lamlash in the Frith of Clyde ; 

 is met with in the Oirleton hills near Haddington, 

 North-hVrwick Law, Traprain Law, and Braid Hills, 

 1 Edinburgh. 



Hnrnslone porphyry. 

 Horn stein Porphir. Werner 



This porphyry occurs in imbedded maatM, beds, and 

 "7- vein*, along with clay-atone porphyry, and in similar 

 MUMMM, both geogiKHtically and geographically. 



7. Pitchttone. 

 Pechstein. Werner. 



This rock, of which description is given in the 

 oryctognostic part of this article, occurs in consider- 

 able abundance hi the form of beds and vein* in red 

 sandstone, in Arran, and other districts in Seat- 



YOU XIV. PART II. 



8. Pitchstone Porphyry. 



Geognosy. 



Pitchstone 

 porphyry. 



Pechstein Porphir. Werner. 



This rock, which has a base or ground of green or ' 

 black pitchstone, always contain imbedded grains and 

 crystals of felspar, which is generally the glassy kind. 



Structure. It occurs in globular, columnar, and ta- Structure, 

 liular concretions. 



Imbedded Minerals. Besides felspar it sometimes Imbedded 

 contains imbedded calcedony, common quartz, calca- mineral*. 

 reous spar, and also zeolite 



Gtognostic Situation. It occurs in beds, imbedded Geognostic 

 manes and veins in various secondary trap rocks, also Situation. 

 in red sandstone, and in secondary limestone. 



licographic Situations. It abounds in the island of Geographic 

 Arran, occurs also in Lamlash, and is met with in Situation. 

 Mull, Eigg, Sky, and other parts of Scotland. 



V. Formations above Chalk, or Paris Formation. 

 Terrain Tertiaires. Daubuisson. 



Under this division we include all the different se- Frmationi 

 condary bed* which are of posterior formation to chalk. above 

 They are principally marl, clay, and sand, interstrati- r p*' f ' 

 fied with beds of limestone, sandstone, and gypsum. m " l 'j on r 

 The only metalliferous minerals they contain are iron- 

 pyrites, and brown ironstone, but many of them a- 

 bonnd in organic remains. This set of rocks appears 

 more of a local nature than any of those hitherto de- 

 scribed. The following description is illustrative of this 

 formation as it occurs around Paris. 



Geographic Distribution. It extends all around Pa- Geographic 

 ris ; to the north, as far as Sciilis and Laon ; to the diiiribu. 

 east, to Rheims and Epemay ; to the south, to Orleans ; " on - 

 and to the west, to Chartres and Mantet. It may be 

 considered as composed of seven systems of beds, viz. 



1. Plastic day with sand. 



8. Coarse limestone, or limestone with cerites, and 

 accompanying sand and rsmUtimfr 



3. Siliceous limestone. 



4. Gypsum and marl 



6. Sand and Sandstone. 



7. Fresh-water limestone and mill-stone or buhr- 

 stone. 



The chalk on which they rest present* numerous 

 inequalities in and over which these beds are arranged, 

 and generally in a horizontal or slightly inclined po- 

 sition. 



1. Plastic Clay and Sand. 



Thi* bed, which re.ts immediately upon the chalk, Flattie 

 consists of an unctuous, tenacious, and variously co- clay and 

 loured clay, employed by putters, arid named by Brong- **"* 

 niart, plastic clay. It contains little chalk, but is fre- 

 quently intermixed with sand, particularly towards its 

 upper part ; sometimes this sand is divided into two 

 beds. It varies in thickness, in some points not ex- 

 ceeding a few inches, in others being many fathoms. 

 It contains few shells, and these are marine. 



2. Coarse Limestone, with Sand and Sandstone. 



Above this clay is a bed principally of a calcareous Coutt 

 nature, composed of an alternation of beds of coarse limwtonr. 

 limestone, marl, and slate-cUy, which occur always with nd 

 in the same order, over an extent of 25 leagues of h < 1 "*<> 

 country. The average thickness of the whole together " on 

 is about 90 feet. 



The lower beds are very sandy, and often contain 

 grains of a green matter, resembling that found in the 

 Si 



