10 GEOLOGICAL MEMOIRS. 



blende, mica, and magnetic iron, also quartz and garnet, besides 

 nodules of opal, &c. [Group 1. Sanidine-tuff. Trachyte-, phono- 

 lite-, immice-tuff, and alumstone in part.] 



2. Grey to blackish-brown, earthy and soft, wacke-like matrix. 

 Contents : numerous crystals and fragments of augite, hornblende, 

 magnetic iron, rubellan, and calc-spar, also of basalt and leucite. 

 [Group 2. Basalt-tuff. Basaltic and doleritic tuff, peperino, and 

 p alagonite- tuff. ] 



3. Distinct or indistinct slaty or fine earthy matrix, generally 

 effervescing with acid and partly soluble ; green or grey, yellow to 

 brown-red ; containing limestone ; and resembling diabase-tuff or 

 clay-slate ; enclosing layers, nests, or grains of calc-spar, and often 

 also plates of clay- and chlorite-slate. [Schalstein in part.] 



II. Order. Tufas, with a matrix similar in composition to the en- 

 closed fragments, and which but rarely or never enclose crystals of 

 other minerals. Closely allied to the Tufas of Order I. 



1 . Matrix : more or less earthy, of a clayey nature, dense or porous, 

 grey, or yellowish to brown. Contents : various- sized, generally half- 

 weathered fragments of trachyte, pumice, or phonolite. [Group 3. 

 Sanidine-conglomerate. Trachyte-, phonolite-, pumice-conglomerate, 

 and trass.] 



2. Matrix : earthy, of a calcareo-argillaceous nature, greyish- 

 brown, yellowish, or earth-coloured. Contents : half-weathered, 

 rounded blocks, pebbles, or grains of basaltic and other rocks. 

 [Group 4. Basalt-conglomerate.'] 



3. Matrix : soft, often slaty, consisting of earthy diabasic detritus, 

 often calcareous, greenish-grey, dirty-green, or leather-brown. Con- 

 tents : rounded fragments and grains of diabase. [Group 5. Chlo- 

 rolite-conglomerate. Diabase-tuff and diabase-conglomerate .] 



4. Matrix : consisting of fine indurated orthoclasic rocks, often 

 areno-argillaceous in character. Fragments of gneiss, granite, por- 

 phyry, and syenite. [Group 6. Orthoclasite-conglomerate. Gneissic, 

 granitic, syenitic conglomerates, andfelsite-tufa or clay-porphyry.] 



III. Holoclastic Eocks. 



I. Order. (Conglomerate.) Fragments at least as large as a hazel- 

 nut. 

 a. Simple. Fragments derived from one variety of rock. 



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

 Argillaceous conglomerate, containing either quartzite, gneiss, 

 granite, clay-slate, porphyry, or mica-schist.] 



2. With calcareous matrix. [Group 2. Calcareous conglome- 

 r rate. Siliceous and phonolitic conglomerates.] 



