OPPONENTS AND OBJECTIONS. 185 



" 4th. The ' chamber casts ' being composed occasionally of 

 loganite and malacolite, besides serpentine, is a fact which, 

 instead of favouring their organic origin, as supposed, musTi 

 held as a proof of their having been produced by mineral 



jtencies; inasmuch as these three silicates have a close 



judomorphic relationship, and may therefore replace one 



lother in their naturally prescribed order. 

 6th. Dr. Giimbel, observing rounded, cylindrical, or tuber- 



ilated grains of coccolite and pargasite in crystalline cal- 



[•eous marbles, considered them to be 'chamber casts,' or 

 organic origin. We have shown that such grains often 



*esent crystalline planes, angles, and edges ; a fact clearly 

 proving that they were originally simple or compound crystals 

 that have undergone external decretion by chemical or solvent 

 action. 



*' 6th. "We have adduced evidences to show that the ' nummu- 

 line layer' in its typical condition — that is, consisting of 

 cylindrical aciculi, separated by interspaces filled with calcite 

 —has originated directly from closely packed fibres ; these 

 from chrysotile or asbestiform serpentine; this from in- 

 cipiently fibrous serpentine ; and the latter from the same 

 mineral in its amorphous or structureless condition. 



" 7th. The ' nummuline layer,' in its typical condition, un- 

 mistakably occurs in cracks or fissures, both in Canadian and 

 Connemara ophite. 



" 8th. The ' nummuline layer ' is paralleled by the fibrous 

 coat which is occasionally present on the surface of grains of 

 chondrodite. 



" 9th. We have shown that the relative position of two super- 

 posed asbestiform layers (an upper and an under ' proper 

 wall '), and the admitted fact of their component aciculi 

 often passing continuously and without interruption from one 

 'chamber cast' to another, to the exclusion of the 'inter- 

 mediate skeleton,' are totally incompatible with the idea of 

 the 'nummuline layer' having resulted from pseudopodial 

 tubulation. 



" 10th. The so-called * stolons ' and ' passages of communi- 

 cation exactly corresponding with those described in Cyclo- 



