12 GEOLOGICAL MEMOIRS. 



(unequal parts of clay and sand) and loam (equal parts of 

 clay and sand). 



b. Calcareous. 



aa. Calcareous clays, more' or less plastic, with at most 15 

 parts of lime, and at least 75 per cent, of clay. Common 

 and marly clays. 



bb. Marl. Scarcely adhesive or plastic, with at least 15 per 

 cent, of lime, and at most 75 per cent, of clay. 



Clay-marly 25-50 per cent, lime ; 50-75 per cent, clay ; 

 0-5 per cent. sand. 



Loam-marl (loess), 15-30 per cent, lime; 10-40 per 

 cent, clay ; 25-50 per cent. sand. 



Calcareous Marl, 50-90 per cent, lime ; 10-40 per cent, 

 clay ; 0-20 per cent. sand. 



Bolomitic Marl, 10-30 per cent, lime ; 10-40 per cent, 

 carb. magnesia ; 20-50 per cent, clay ; 0-30 per cent, 

 sand. 



II. Organo-mineral soils. Composed of organic and mineral 

 matters : greyish-black to blackish-brown. Losing colour on heat- 

 ing, and giving a brown solution on boiling with potash. 



c. Carbonaceous soils. Clays, letten, loam, or marls, mixed 

 with more or less humus. Humus-, marsh-, or turf-soils. 



THE ORGANIC ROCKS.— I. Class. Anthracides. 



Anthracitic or carbonaceous rocks, as products of organic decom- 

 position, principally of plants. Compact ; with or without visible 

 organic structure ; brown or black ; lustrous or dull. 



The Anthracides are divided into two orders, — 1. the perfect or 

 true coals, not containing ulmine ; 2. the imperfect coals, or those 

 containing ulmine. 



The first group comprises two kinds, viz. the anthracites, such as 

 the graphitic, common, slaggy, prismatic, fibrous, and wood-like 

 varieties of anthracite ; and the coals proper, such as the cannel, 

 glance, slaty, thick-bedded, fibrous, and sooty varieties. 



The second group, or those without ulmine, are such as the brown- 

 coals or peat. The former afTord as varieties, pitch-coal, and the 

 common, flat, woody, needle, paper, waxy, earthy, and other brown- 

 coals. Amongst the latter the author enumerates pitch-turf, sward- 

 turf, paper-turf, turf-earth, mud-turf, and vitriol-turf. 



II. Class. Zoogenites. 



Aggregates, showing more or less clearly animal structure, and 

 possessing always the chemical composition of animal substances. 



1 . Coprolitic rocks ; nodule3 with phosphatic matter. 2. Infu- 

 sorial rocks. rj. Morris.] 



