6 ROCK-METAMORPHISM. 



the present minerals would occur with evidence of their having 

 been in a fluidal or gelatinous condition. Thus it is that ser- 

 pentine, pyrosclerite, saponite, deweylite, and some others are 

 frequently seen occupying what may be considered to have been 

 cracks, cavities, and other openings ; while their substance has 

 a streaked, wavy, or an irregularly netted appearance, as if it 

 had flowed, sometimes continuously, at other times intermit- 

 tently, into these receptacles, or had been deposited on their 

 sides *. In connexion with this matter it may be mentioned 

 that Alphonse Gages has succeeded in making a gelatinous 

 substance with the composition of deweylite "\. It has often 

 been stated that serpentine has infiltrated itself into tubuli and 

 canals of shells and other organisms ; but it is extremely doubtful 

 that the substance, so called, was originally any thing else than 

 an aluminous ferrugino-alkaline deposit, which has become 

 changed into some variety of glauconite { . 



Though serpentine is characteristically colloidal, that is, with- 

 out crystalline structure, other forms (allomorphs) and related 

 varieties are known. Thus chrysotile, thermophyllite, marmolite, 

 metaxite, and flocculite are respectively asbestiform, columnar, 

 laminar, dendro-foliaceous, and granular or floeculent. 



Certain serpentine minerals, as ripidolite, 'are characteristi- 

 cally crystallized. But, as will be more fully explained here- 

 after, there are others, e. g. pyrallolite, picrosmine, bastite, 

 rennselaerite, loganite, &c., including the type species, which 

 occasionally present themselves under crystalline forms : in such 

 minerals, however, more or less of their original substance has 

 been removed ; or it has become serpentinized through chemical 

 changes. 



It would not be difficult to name some fifty or more kinds of 

 hydrous silo-magnesian minerals that have serpentine for their 

 type, and belonging in most cases to both sections of ophites. 



Passing to the mineral carbonates (which, with the silicates 

 already mentioned, constitute the silo-carbacid ophites), these 



* Philosophical Magazine, 5th ser. vol. ii. pi. 2 (bottom of plate), p. 283. 



t British- Association Keport, 1863, p. 204. 



t I have elsewhere mentioned that the spines of a palliobranch (Siphono- 

 treta) contain an infilling consisting apparently of " one of the numerous 

 varieties of glauconite " (W. K.) : see Geol. Mag. new ser. 1877, vol. iv. p. 14; 

 also Introduction, A.D, 1878. 



