MINERALOGY. 



407 



ure 

 crust 



f the 

 lobe. 



Lydian stone in clay-slate, are examples of this kind. 

 Beds composed of various minerals sometimes occur in 

 different rocks. These minerals are usually those of 

 which tiie rook i-> principally composed, irregularly 

 mixed, or are simple mineral;. Such beds are usually 

 very irregular, do not extend through the whole rock, 

 and" in general exhibit apparently great irregularity in all 

 their relation". They have been, but rather improperly, 

 /< ked*. When single beds are well 

 distinguished by the kind of stone of which they are 

 composed, and > nposition shews certain peculi- 



. (as, for example, the determinate presence of me- 

 tallic fixsil*. fee.) they art referred to the particular re. 

 poiiloriet. Beds of iron-pyrites and magnetic ironstone 

 are of this kind. 



Structure of the Crust of the Globe. 



The fourth and last kind of structure we have to 

 describe, is by far the most extemive and important. 

 It is the structure of the crust of the globe itself, in to 

 far as it is composed of rook-formations of different 

 magnitude*, laid over each other in certain directions. 



ler the five following heads, Werner comprehend* 

 every relation respecting the extent and relative posi- 

 tion of formations in general. 



1. The original extent of formations. 



2. Their present extent and continu ty. 



S. The position and direction of the strata of forma- 

 tions, in respect to the fundamental rock. 



4. The direction of the strata themselves, without re- 

 ference to the fundamenta rock. 



5. 1'he relation of the outgoings of the strata to the 

 exterior of the mountain. 



It may be previouOy remarked, that when one forma- 

 tion lies on another, it is said to ret! on it, and the rock 

 on which it rest* is termed the Jnhdamenlal rock ; and 

 tiie plane which separate* the fundamental rock from 

 the formation that covers it, is denominated the plane 

 iralion, which is always parallel with the seams 

 of the strsta. See PUte ( < ( \( V. Fig. 1. 



1. The Original Extent of Formation*. 



Werner observes, that the greater number of forma- 

 tions appear to have been very widely deposited ; and 

 the** be denominate* L'nirertal Formation*. 

 other l>een partially deposited, 



and theo he terms partial or a nommhiu formation*. 



'luilioni extend around the whole 

 (not, however, without interruption), and con- 

 far the greater part of the ma** of which it* 

 crust . d Almost all the primitive, ti 



tioii. and secondary formations, are universal deposi- 

 tions ; of these we may mention granite, gneiss, por- 

 phyry, anil limestone. 



' 'motion* occnr only in particular places, 

 and appear to owe their existence to particular and lo- 

 cal cau'es, for example, to depositions in lakes. La- 

 iiion. that tiie gj |>-urn formation around 

 Pan- .!. 'in the waters of a lake which tor- 



inerly occupie I that part of France; and the t 

 ive local formation in the Isle of Wight and the op- 

 posite coa ,nd, appe ir< ul-n to be a lake for- 

 mation, itia, there is an example 

 of a parti; ::. It consist* of sandstone, lime- 



stone, bituminous-shale, and iron-clay ; and these rest Geognosy. 

 on loose sand. The sandstone resembles in many re- "~ f ~ m 

 spects that found ia other sandstone formations ; yet LATE 

 it does not belong to any of them, as is evident from 

 its position; and the rocks with which it i? associated. 

 Werner conjectures that it may have been formed by 

 a small and initial flood. 



The examination of these partial appearances is of 

 much importance, not only in extending our know- 

 ledge of the variety of formations, but in connecting 

 the history of the earth more nearly with that of man. 



2. The Pretent Extent and Continuity of Formation*. 



The present extent and continuity of formations is The p. 

 very different from what it was originally. We find scnt *"' 

 them eilher extended uninterruptedly over great tracks *"^ t ' n f u " 

 of country, or they appear isolated, of little extent, f ornut i 0al . 

 and frequently resembling partial formations. In the- 

 one case, they are said to be unbrnken, in the other 

 broken. The broken formations occur in small detach- 

 ed manes; and 'these have peculiar denominations, 

 according to their position and shape. 



When detached portions occur on the summits of 

 hills, these are called <,//. Fig. 3. a. When portions Fig. I.*. 

 occur, filling up hollow spaces between mountains, 

 they are denominated Ufi/Mingt, Fig. 2. 6. And Fig. 9. 6. 

 when a portion occurs only on one side of a mountain, 

 it i* said to be thield-formtd, Fig. 2. c. or to have f lg . f. r . 

 the shape of a shield. 



3. ThePotilio* and 1- ./" Strata in regard to Ike 



Fundamental Ruck. 



When strata have the same direction as the funda- The poti- 

 mental rock, they are said to be conformable with it, >">nind 

 Fig. 3. a. if the direction is different, they are said to be <"r-tion of 



uiKonl'urmalil,-. if they differ only in direction, we say itrala in 

 ' _fi- r:_ a i . i.... rVKfartto 



KjarmabU, Fig. 3. b. ; but if -". 



that they are iimp> . . _ ,, , 



they diner not n v .n d but lie over the ends mcntti 



of the strata of the fundamental rock, they are said rock. 

 t i be unconformable i.iul ovtiljing, Fig. 3. f. Overly. Fig. 3. . 

 ing strata occur more fn '!ian simply uncon- *''** 



form ible, and have far greater extent. 



4. Direction of the Strata tfie-mtrlret, nilhovi reference to 

 i lie Fundamental Rock. 



Direct ionof 

 the strata 

 lherne)e* 

 without 

 reference 

 to the fun- 

 dirmnlal 

 rock, 

 fig. 4. 

 Fig. 5. b. 

 Fig. 8. 



Fig. T. a. 

 Fig. 10. 

 r ig. 8. I: 



Strata are either ttmi^fil, that is, disposed in one 

 direction on the fundament . I r-n-k. Fig. 4 or they 

 turn around it, and inclose it ; in this latter case they 

 are said to be mantlr-lormtd, or manlle-thaped. Fig. 

 5 b. If the strata are not only wrapped around the fun- 

 dwnetital rock, but also cover it* extremities, they are 

 amid to be taddle-jttaped, Fig. 6 



When the upper part of the saddle-shape is carried 

 away, the manllf-shn; t is formed. 



ita are sometime* concave, and they are then said 

 to be hann thaped, Fig. 7 <' ; t'i. 10. but if the conca- 

 vity be oblong, they are n-mui Irong/i-thaped, Fig. 8. 6. 

 In tiie concave, that is, the Iw-on and trough shaped, 

 and in the con vex, that is, the saddle and mantle shap- 

 ed strata, the outgoing* * form circlet) : in the concave, 

 the outer and greatest ciicle, according to Wc.ner, is 

 the oldest ; in the convex, on the contrary, the outer 

 and largest circle is considered to be the newest 



V Ik* 



4"iyr<fe*tTMa an aadrntoot their opsw extremities a* thty appw tt the nrfaec of the earth. F%- 9. 



