SENFT ON ROCKS. 11 



3. With carbonaceous matrix. Bleaches on heating. [Group 3. 

 Coal-conglomerates ^\ 

 $. Compound. Fragments derived from various rocks. 



1. "With argillaceous or areno-argillaceous matrix. [Group 4. 

 Argillaceous conglomerates, with quartz, gneiss, &c, quartz, 

 granite, &c, or granite, syenite, &c] 



2. With areno-calcareous matrix, and fragments of sandstone, 

 limestone, &c. [Group 5. Calcareous conglomerate, contain- 

 ing various rocks. Nagelfluh and Bone-breccia.^ 



II. ^Order. Fragments about the size of a pea, generally consisting 

 of grains of quartz, mica, and felspar. (Sandstones.) 



a. Argillaceous matrix. Kaolin-sandstone, common clayey sand- 

 stone, siliceous clayey sandstone, and ferruginous sandstone. 



b. Calcareous matrix. Calcareous, marly, and green or glau- 

 conitic sandstones. 



c. Carbonaceous or bituminous matrix. Bituminous and asjphaltic 

 sandstones. 



III. Order. Slaty rocks, generally grey to black. (Slates.) 



a. Argillaceous. Principally clayey, mixed with mica and sand ; 

 grey to reddish. Greywacke-, clay-, or alum-slates and slaty 

 clay. 



b. Marly and sometimes bituminous. Marl- and bituminous marl- 

 slate (copper-slate). 



c. Highly carbonaceous. Carbonaceous slates. Coal-shale and 

 brandschiefer. 



DETEITAL ROCKS. 



A. Formed by the mechanical fracture of rocks. Detritus. 



1. Volcanic or eruptive detritus. Principally formed by the 

 destruction of lava in the volcanic crater. Lava blocks and bombs, 

 lapilli, and lava sand and ash. 



2. Weathered detritus. Formed of various rocks. Blocks, gravel, 

 and sand. 



B. Earth and soils, partly arising from chemical decomposition. 

 Loose, crumbling or friable aggregates, cohering when damp. 



I. Purely mineral soils. Not becoming paler on heating, and 

 not forming a brown solution when boiled with potash. 

 a. Argillaceous. 



aa. Fat clays; tenacious, containing little or no sand. Slightly 

 adhesive, unalterable by heat. Fuller's earth and kaolin. 

 Strongly adhesive and alterable by heat. Clay, 

 bb. Meagre clays, containing much coarse sand. Let ten 



