352 ME. J. W. GREGORY ON THE 



already referred to, though as the bedding-planes do not come out 

 clearly till the surface be wetted, they are not well shown. The 

 explanation of the relations of the bedding-planes to the calcite- 

 bands on the organic hypothesis is beset by three difficulties: 1st, 

 it requires that this thin strip of Eozoon should have been buried 

 vertically, which, considering its proportions, is not very probable ; 

 2nd, had it been covered by the deposition of a calcareous mud we 

 might have expected this to have been piled up around it, so that 

 the stratification should not meet it with such regularity ; and 3rd, 

 had the body-chambers been filled by the washing in of the lime- 

 stone material, any planes of bedding would have accommodated 

 themselves to the irregularities of the cavities, and the bedding 

 would hardly have been continued so exactly in the same straight 

 line across all the layers traversed by any plane. It seems to the 

 writer quite impossible to account for the continuity of the bedding- 

 planes across the specimen, except on the view that the calcite-bands 

 have been formed later than the dark layers of amorphous carbonate 

 of lime between them. 



The fact that the cleavage-planes are not continued across the 

 calcite and that no mica has been developed in this would alone be 

 sufficient in the minds of many geologists to settle the relative ages 

 of the crystalline and amorphous parts of the limestone. But it 

 cannot be expected that those who regard the foliation of the pre- 

 Cambrian schists as an original structure in the rocks will attach 

 much weight to this argument. 



(d) The Origin of the Calcite-hands. — It now remains to be con- 

 sidered what explanation of the origin of the crystalline calcite can 

 be offered without the assistance of any organic agency. Profs. 

 King and Rowney suggested that they were formed by the infil- 

 tration of calcite into a series of cracks, but this is not an adequate 

 explanation. In some cases a small patch of the calc-micfi-schist 

 can be seen completely surrounded by the calcite, and this alone is 

 sufficient to overthrow the fissure hypothesis : moreover, the remark- 

 able irregularity of the junction of the crystalline and amorphous 

 carbonate of lime, the distribution of the graphite particles in the 

 former, and the absence in it of any banding, are all difficult of 

 explanation on this view. 



It seems more probable that the calcite-bands were formed by 

 the solution of the limestone and its redeposition along the lines on 

 which the water percolated through the rock. To explain why 

 these curved bands were formed is probably impossible without a 

 knowledge of the posit iou which the slab occupied when in situ. 

 The whole surface of the specimen has been slightly altered to a 

 depth of half an inch. The irregularity and apparent capriciousness 

 of the action by which the bands were formed are too well known 

 for any serious objection to be raised to this explanation while the 

 field relations of the specimen are unknown. In most cases the 

 solvent has acted along the lines of weakness and started from the 

 weathered surface. As a rule, the secondary calcite has been deve- 

 loped along the bedding-planes, but at times some has also been 



