202 ME. E. B. WETHEKED ON THE [May 1895, 



was continuous, but that it has been destroyed. Of this there is 

 no proof. What evidence there is as to the origin of the crust 

 leads to the inference that the granule has been formed by tubules 

 growing round a nucleus without any system of regularity. In 

 support of this contention I would draw attention to the outlines 

 of tubules in the non-concentric part of the crust, and to the fact 

 that these ' crop up,' as it were, and do not run around the nucleus 

 in the same concentric system as those in the other part. 



I have before referred to a feature remarkably well illustrated 

 in PI. VII. fig. 6 (b), namely, that the calcium carbonate in oolitic 

 granules where the concentric layers are ' clear ' is usually present in 

 two forms, namely, the granular amorphous and the non-crystalline 

 clear, the latter representing the actual structure, and the former 

 infilling or secreted material. This is inconsistent with the con- 

 cretionary theory of the origin of oolitic granules. If this latter 

 process were the true one, then the calcium carbonate would be 

 present in the form of ordinary carbonate of lime, which the amor- 

 phous substance really is. Doubtless molecular changes have taken 

 place, but these would not explain the condition of things in fig. 6, 

 nor in any of the others that I have examined. I have noticed no 

 disposition of the amorphous calcium carbonate to alter even into 

 calcite. If we take PI. VII. figs. 4, 6, and 9, the secreted or in- 

 filling carbonate of lime shows distinct differentiation, and there is 

 no sign of transition into calcite nor into the fibrous structure which 

 is so characteristic of the granules (fig. 9). 



Much of what I have said with regard to fig. 6 applies also to 

 fig. 4, but the difficulty of assigning the origin of the granule to 

 chemical concretion seems to me to be increased. Here we have an 

 oolitic granule which shows concentric lamination in part of the 

 crust ; but half is devoid of this feature, and in place of it we see 

 a mass of more or less oval spots surrounded by non- crystalline 

 clear 2 calcium carbonate. 



The concentric laminse are also studded with spots which must 

 have a meaning, as they occur, in some form or other, in most 

 oolitic granules, no matter from what geological formation the 

 oolite may be taken. 



Further, it cannot be doubted that there is some connexion 

 between these spots in the concentric strata and those in the non- 

 concentric part. I think, too, that any impartial observer would 

 admit that the dark portion is very suggestive of the infilling by 

 inorganic material of organic structure, the surrounding semi-clear 

 calcium carbonate representing the skeletal structure. 



This view, expressed of the organic origin of the granule in 

 PI. VII. fig. 5, is supported by fig. 7. The structure exhibited by 

 this latter granule is strikingly like the non-concentric part of the 

 former one ; in fact, had fig. 5 been cut across the non-concentric 

 part, then we should have had a structure similar to that shown in 

 fig. 7. If we admit, which I think we must, that the last-mentioned 



1 As seen by reflected light. 



