C.e-inojT. 



Brown 

 ml, Mio- 



which the organic remains are said to be entirely ma- 

 rt**. The second bed contains the lower siliceous lime- 

 stone and the lower gypsum and marls, both of which 

 contain scarcely any other petrifactions than those of 

 land and fresh water animals ; and hence is called a 

 fresh wmter formation. The third bed is composed ot 

 the superior marls, sands, and sandstones, and the few 

 petrifactions it contain* are of marine shells. Lastly, 

 the fourth bed it a great fresh nater formation. 



A series of rock*, possessing many of the characters 

 of those around Paris, occurs in the Isle ot Wight, 

 and the neighbouring districts in the south of Eng- 

 land, and ha* been well described and illustrated 

 by an excellent man and good observer, Mr. Webster of 

 the Geological Society of London. Beudant describes 

 rocks of the same nature as occurring in Provence, :ind 

 informs us that the famous quarries ot'Aix, which afford 

 BO many different kinds of petrified fishes, are situated 

 in a marl belonging to the Paris formation. The fa- 

 moo* district of Oeningen on the bank* of the Lake 

 of Constance, so well known to naturalists on account 

 of the great variety of petrifaction* it affords, agrees 

 in iu general character* with the Pari* formation. 

 The fresh water limestone, has been found in Aurergne, 

 in the vicinity of Montpellier, to the north of Tarn, 

 between Montauban and Agen ; also in Spain, in the 

 vicinity of Burgos and Seville ; in Germany, near Ulm ; 

 and in Italy, in the Roman State*. 



8. Brown-Coal, associated nith Rockt above Ckali. 



Associated with a group of rock* above chalk, there 

 are sometimes extetuive formations of brown-coal. 

 """ There is a fine example of this arrangement of bn.w n- 

 2^! *"*"" coal in the North of France, in the country extending 

 from Beauvai* to the vicinity of Rheims. There are five 

 beds of brown coal, varying from two to six feet in 

 thickness ; and are separated from each other by layer* 

 of gravel and loam. Both the coal and the layers be- 

 tween it are impregnated with iron pyrite*. The 

 whole i* covered with beds of marl and limestone ; 

 those bed* which rest immediately upon the coal, con- 

 tain fresh water shell*, while those at a distant, 

 it include marine shells; and it i said that the up|>er- 

 most part i* a shelly sandstone. M. Marcel de Serre* 

 inform* us, that in the vicinity of Beziers fresh water 

 shells are found in a bed of brown coal, which is 

 covered by bituminous bed*, bituminous limestone, 

 with fresh water shells, compact limestone, without 

 shells, and, lastly, with a limestone containing impres- 

 sions of cerites. Sometimes thi* brown coal i* covered 

 with trap-rock* or lavas. 



The brown-coal formation contains a few imbedded 

 minerals, such as iron-pyrites, bog-iron-ore, selenite, 

 honey-stone, retin-asphalt, and a mineral of an inflam- 

 mable and waxy nature. 



CLAM IV. ALLUVIAL ROCK*. 



Alluvial Thi* class comprehends those rocky substances form- 

 rock*, ed from previously existing rocks, of which the'mate- 

 rials have been broken down by the agency of water 

 and air ; they are therefore generally loose in their tex- 

 ture, and are never covered with any real solid and 

 rocky secondary strata. 



Werner divide* them in the following manner: 



Mountain ! Mountain alluvial formations. 

 alluvial . () n the summits of mountains, 



formation*. 5 () th e ^jj, o f mountain*, and at the foot of 

 mountain range*. 



Geognosy. 



Alluvial 

 formations 

 of low or 



MINERALOGY. 435 



2. Alluvial formations of Ion or fat lands. 

 1. Mountain alluvial formations. 



a. On Summit* of Mountains. 



The alluvium found on the tops of mountains, and flat lands, 

 mountain-chains, consists generally of a thin bed form- On turn- 

 ed by the decomposition of the immediately subjacent miu of 

 rocks. This bed, particularly when covered with ve- mountains, 

 getable matter, forms a coat which long protects the 

 solid strata from the wasting influence of the weather. 



b. In Valleyt. 



The disintegrated rocks on the sides of valleys, (n n e ,,. 

 yielding to their own weight, or carried downwards by 

 torrents, are stopped at the foot of the mountain ; they 

 are accumulated there, and, in the course of time, form 

 a deep protecting cover for the lower part of the moun- 

 tain, and fill up the bottoms of the valleys. 



r. At the foot of Mountain Ranget. 



Besides the-ftlluvial covering on the bottoms of val- At the foot 

 leys, and on the basis of their bounding hills and moun- of moun- 

 tains, there often occurs very extensive alluvial forma- uin 

 tions, extruding to a greater or lesser distance from the 

 general foot of the acclivity of the great mountain- 

 chains, or mountain groups. These formations are com- 

 posed of fragment* of the neighbouring mountains, but 

 are arranged in a vast horizontal Ixxl ; thus intimating 

 that they must have been levelled by die action of a 

 great mass of water, in the form of a lake or inland sea. 

 The plain* of Piedmont and Lombardy, at the foot of 

 the Alps, present a colossal example of this kind of al- 

 luvial formation. 



8. Alluvial formation* of the low or flat lands. 



The alluvial sub-stances met with in the great plains, Alluvial 

 are principally sands and clays of different descriptions, foimatmnt 

 Theme occasionally include various minerals, such as of tlic low 

 calcareous tuffa, peat, &c. 



-hall first describe the sand and clays, and after- 

 wards the calcareous tuffa, and other subordinate sub- 

 stance* met with in them. 



a. Sand. 



Sand, a* is well known, is formed of small gram* 

 supposed to have been derived from previously existing 

 rocks of a quart zy nature. It sometimes covers im- 

 mense tract* of country, and form* great deserts, a* 

 those of Barbary and of Arabia. 



The extreme fineness of the particles renders the 

 Miid moveable by the slightest breath of wind, so that 

 when the storm rages, the desert present* a picture 

 of moving waves, mountains, and pillars that baffle all 

 description, and which overwhelm vast tracts of country 

 carrying every where desolation and destruction. 



Down*. When the ** eoait i* low, and the bottom Down*, 

 consists of sand, the wave* push this sand towards the 

 shore, where, at every reflux of the tide, it become* 

 partially dried; and the winds, which almost always 

 blow from the sea, drift up some portion of it upon the 

 beach. By this means, doimt, or ranges of low sand 

 hills, are formed along the coast. These, if not fixed 

 by the growth of suitable plants, either disseminated by 

 nature, or propagated by human industry, would be 

 gradually, but certainly, carried toward* the interior, 

 covering up the fertile plain- with their sterile particles, 

 and rendering them unfit for the habitation of mankind ; 

 because the same winds which carried the loose dry 

 (and from the (bore to form downs, would necessarily 



4 



