66 OUTMM - <M 1 1 1 'MI-GEOLOGY 



of the loose dust and blocks ejected by a volcano. 

 To these the general term Tuffs has IK en applied 

 (Fig. .o). 



With the fragmcntal rocks may be classed those which 



been formed of the fragmentary remains of plants 



(Fig. n) and animals. Ordinary crinoidal limestone 



(Fig. 15) is a characteristic example, consisting as it does 



FIG. ii. Piece of coal, composed of matted stems of Sift'Maria and 

 Ltf>i<io<ie>tdron. Carmarthenshire. (Dc la Beche.) 



of the congregated joints and plates of encrinites, \\\\\\ 

 more or less perfect mollusca, corals, echini, fish-teeth, 

 etc. Some of these organically -derived rocks, how- 

 ever, possess textures which would justify their being 

 called compact rocks, as in the case of cannel coal. 

 Others again, have acquired, in large measure, a 

 crystalline texture, as has happened so abundantly in 



