THE FARMER'S MAGAZINE. 



23 



cession of strata, called guciss, mica slate, quartz- 

 rock, and crystalliue limestoue or marble. Gneiss is 

 a stratified rock, coutaiuiug the three constituents of 

 granite — quartz, felspar, and mica — arranged in sepa- 

 rate layers, instead of irregularly, as in granite. 

 Quartz-rock is a siliceous rock, having the aspect of 

 a very hard sandstone, Crystalline limestone is too 

 well known as statuary marble to require description. 

 So much for the divisions of the azoic strata. 

 These, and in fact the whole of the stratified series, 

 consist of numerous clayey, sandy, aud calcareous 

 strata, frequently repeated, of different degress of 

 liardness, and combiued in different proportions. 

 According to the peculiarities of these fossil contents 

 they are divided into minor groups or systems. The 

 palfeozoic divisionjconsists of four systems : 1, the 

 Cambrian; 2, the Silurian, upper and lower; 3, the 

 Devonian; 1, the Carboniferous; 5, the Permian. 

 These names, with the exception of the carboui- 

 ferous, are all geographical ; tiiatis, they are derived 

 from those countries where they are best exhibitci, 

 or were first described. These are called their typi- 

 cal regions. The lower part of the Silurian system 

 is disputed territory. Sir Hoderic Murchisou and 

 the government geologists restrict the term Cam- 

 brian to that thick mass of non-fossilifcrous strata 

 which contains the celebrated roofing slates of 

 Bangor, Llauberris, and Ffestiniog, in North Wales, 

 aud of Skidaw in Westmoieland, in which no fossils 

 have yet been found. They extend the base of the 

 Silurian system down to the lingula bed, which con- 

 tains the first known traces of organic life in the form 

 of shells of the genus Lingula. Professor Sedgewick, 

 on the other hand, who was the first to iuvestigate 

 this lower part of the stratified series, makes the 

 Ca iibrian system include the lower half of the 

 Silurian system, where a change takes place in the 

 character of the fossils. We believe this to be the 

 most proper division; but in science, as in other 

 matters, possession is nine points of the law. The 

 government geologists are in possession of this lower 

 part of the fossiliferous rocks, aud appear likely to 

 retain them — at any rate, for the present. 

 The Devonian, which reposes on the Silurian system, 

 has only risen into its due importance of late. It was 

 long considered destitute of fossils, and deemed a 

 subordinate member of the carboniferous group 

 uuder the name of the Old lied Sandstoue. It takes 

 its present name from Devonshire, where its rocks 

 are highly fossiliferous, though so much altered by 

 contact with igneous masses tfeat they have assumed 

 the characters of the older slates, and were long 

 mistaken for them. In Herefordshire and Scotland 

 it is of great thickness, aud occurs under its original 

 name of the Old lied Sandstone, where it has been 

 reudered famous for the fossd fishes with which it 

 abounds, wliich have acquired celebrity from that 

 delightful little work of Miller— "The Old Red 

 Sandstone, or New Walks in an Old Pield." 



The carboniferous system takes its name from the 

 coal strata, of which it is the seat. The rich beds 

 of coal in most parts of the world belong to this part 

 of the series. The carboniferous era was one of 

 rank vegetation of a peculiar character, whose accu- 

 mulated remains have produced the valuable coal 

 fields of England and North America. There are a 

 few instances of thin and inferior beds of coal in 



other parts of the series, but they_ have rarely been 

 worked to advantage, and never in districts acces- 

 sible to the produce of the true carboniferous series. 

 The sums of money which have been squandered in 

 fruitless trials for coal, from the waut of this know- 

 ledge, are incredible. 



The Permian system takes its name from the 

 province of Perm, in Russia, where it covers exten- 

 sive areas, aud is richer in fossils than elsewhere. In 

 England, it is feebly represented by our magnesian 

 limestone ; that, and the trias above it, were formerly 

 grouped together under the name of the New Red 

 Sandstone. As its fossils were better known, it 

 became evident that they belong to different periods 

 of organic life — the Permian system to the palgeozoic, 

 the triassicto the mezozoic. , 



We come now to the systems or groups which 

 compose the mezozoic or division of middle life. 

 These, iu the ascending order, are the triassie, 

 before mentioned, the liassic, the oolitic, and the 

 cretaceous. The triassie derives its name from the 

 tlireefold division of this part of the series in Ger- 

 many, where it is more extensively developed, and 

 more fossiliferous than with us. The liassic is so 

 called from the lias, a provincial name for clay, of 

 which iu England it chiefly consists. The name of 

 oolitic was given to the next group of rocks at a 

 time when names founded on mineral , characters 

 were more in vogue than at present. It is derived 

 from a Greek word, signifying an egg, in conse- 

 quence of some of its limestones being composed of 

 rouud concretions resembling the roe of fishes. Tha 

 well-known freestone, of which St. Paul's and some 

 of our public buildings arc constructed, is one form 

 of its limestones. The crumbling stone, of which 

 many of the colleges iu Oxford are unfortunately 

 built, is another. The Yorkshire paving stone is a 

 siliceous form of one of its subordinate divisions, 

 which in the south of England is calcareous. The 

 cretaceous system is so called from the Latin name 

 for chalk, which constitutes one of its principal for- 

 mation. 



Up to this point we have not enumerated the sub- 

 divisions, or formations, composing the difl'erent 

 systems, because they arc not exposed on the sur- 

 face in Kent. In our ascent, liowevcr, through 

 some miles of strata, we have now reached Kentish 

 rocks, and we will i-emind our readers of the 

 subordinate divisions of the cretaceous group which 

 have already been mentioned as constituting part of 

 the strata of the Wealden area. These are the 

 chalk, the upper greensaud, the gault clay, and the 

 lower greensaud. In Kent the upper greensand is 

 merged in the chalk, or forms a very thin band at 

 the base of the chalk escarpment. The strata of the 

 Wealden area, viz., the Weald clay and the Hastings 

 sands, are a local deposit formed in the delta of 

 some large river, like the deltas of the Nile and 

 Ganges. As they contain only the remains of the 

 land and freshwater, it is doubtful whether their 

 contemporaneous beds are to be sought in the chalk 

 or in the oolites. The French geologists — for the 

 Wealden strata eitend into France — have estab- 

 lished a group, to which they refer it under the 

 name of the Neacomiau system. They consider it 

 intermediate between the chalk and the oolites, and 

 as forming the marine representative of the Wealden 



