THE EARTH. 11(3 



Others have fo'ond a different use for them, especially when they 

 run surrounding our globe ; which is, that they stop the vapours 

 that are continually travelling from the equator to the poles ; 

 for these being lu-ged "by the heat of the sun, from the warm re- 

 gions of the line, must all be accumulated at the poles, if they 

 were not stopped in their way by those high ridges of mountains 

 which cross their direction. But an answer to this may be, that 



ler of their names, beginning with the lowest. Tliese are as follow : 1. Gra- 

 nite. 2. Gneiss. 3. Mica-slate, i. Clay-slate. 5. Porphyry and Sienite. 

 Alternating with gneiss, mica-slate, and clay-slate, there occur beds of 

 several other rocks, which being of no great extent compared with 

 being frequently repeated, have been termed subordinate formations. These 

 are primitive lime-stone, primitive trap, quartz, fluity-slate, and gypsum. 

 Along with porphyry and sienite, occur serpentine and granite. Primitive 

 rocks contain no petrifactions. They constitute the highest motintains on 

 the face of the earth. They are evidently chemical compounds, and contain 

 no minerals, which show themselves to have been mechanical depositions- 

 They must have been formed before the earth was inhabited. The transU 

 tion formation consists, likewise, of five classes of rocks, only one of which, 

 namely, grei/ wacke, is peculiar to it, and characterises it. These rocks are 

 as follow : Transition lime-stone. 2. Grey wacke, and grey wacke-slate. 

 3. Transition trap. 4. Transition fluity-slate. 5. Transitio:i gypsum. Pro. 

 fessor Jameson has likewise discovered porphyry and granite among transi- 

 tion rocks. These rocks contain petrifactions of animals and vegetables ; but 

 they are of the lowest order, both of animals and vegetables, and generally 

 consist of species which can be no longer found in a recent state. Hence 

 these rocks must have been formed after the earth contained both animals 

 and vegetables. ITie floetz formation occurs in a level country, and is usually 

 covered by soil. As far as geological knowledge at present goes, it is known to 

 consist of, 1. Sand-stone. Of this there are various formations; three, at least, 

 have been ascertained. The lowest of aU is red, and distinguished by the name 

 of old red sandstone. 2. Lime-stone. Of this also there are at least three forma- 

 tions, if we include chalk, the position of which is not very well understood. 

 3. Floetz gypsum. Of this there are two formations, one of which is dis- 

 tinguished by alternaf ug with rock-salt 4. Floetz-trap. This consists of 

 green stone, and was first observed by Professor Jameson, in his examination 

 of Dumfriesshire. 5. Independent coaL This formation, besides coal which 

 characterises it, contains a variety of other rocks, iu beds chiefly sand-stone, 

 greenstone, clay, iron-stone, lime-stone, and shale. 6. Newest floetz-trap. 

 This formation generally caps the hills in those countries where it occurs. 

 It consists of basalt, wacke, grey-stoue, porphyry-slate, green-stone, trap- 

 tuff, clay-stone, sand-stone, &c. The floetz formations abound in petrifac- 

 tions, and in mechanical depositions. Most of the metallic ores occur in the 

 primitive and transition formations. The alluvial formation consists of the 

 loose soil, gravel, sand, moss, &c. which cover the surface of the earth, 

 and the volcanic formations consist of the ashes and lavas vomited out i>f 

 Tolcauo'is. 



