﻿4 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [NOV. 6, 



be about three millions in a cubic inch. Hence I think it may be 

 safely considered that there are two or three millions of them in a 

 cubic inch of the stone, when it does not contain many larger 

 shells. 



Having thus described these reniform bodies, and shown in what 

 vast numbers they are found, I will consider what they are. First 

 of all, they cannot possibly be grains of sand, because — 



1 . They are much too regular in their form, the most regularly 

 formed grains of sand being somewhat angular. 



2. Their action on polarized light is totally different from that of 

 grains of sand ; which show uniform series of colours with no radi- 

 ating dark and coloured bands, and have each a definite single system 

 of neutral axes. 



3. The agate structure is quite different from that of siliceous 

 sand. 



4. Their appearance by reflected light when mounted in Canada 

 balsam, or seen as thin sections, is milk-white, whereas sand is clear 

 and transparent. 



5. Some of them are filled with calcareous spar, which is also di- 

 stinct in its characters from rounded grains of any kind of calcareous 

 substance likely to occur in such a situation ; but precisely the same 

 as the agatized ones, except in chemical constitution. 



I have had it suggested to me, that they might have been calca- 

 reous concretions, similar to the ovum-like concretions of oolite, sub- 

 sequently converted into agate. They, however, do not appear to me 

 to have been such, because — 



1 . They are not of the form of the ova of oolite, being too reni- 

 form. 



2. Although some are more entirely calcareous, they do not ex- 

 hibit the slightest trace of concretionary structure, but are filled with 

 calcareous spar in the same manner as the chambers of the ammo- 

 nites which are found in this rock. 



3. They are quite distinct from the genuine concretions which 

 may be seen in slices of the stone. 



At first I thought that they might have been globular siliceous 

 spiculse of sponges, but after finding some which were filled with 

 calcareous spar, I abandoned the idea ; for it does not appear to me 

 at all likely that the siliceous matter could have been removed, and 

 its place occupied by calcareous spar. 



It being of course a matter of much interest to learn whether they 

 originally possessed shells or no, I made a thin slice of one of the 

 ammonites which occur in the rock having its chambers filled with 

 calcareous spar, and by examining it by polarized light, I found 

 that where no impurity had entered there was no trace whatever of 

 the shell discoverable, the whole of it having its crystalline particles 

 arranged in the same direction as the calcareous spar in the interior. 

 Where, however, there was muddy impurity in the interior, the shell 

 could readily be distinguished. Moreover, by examining the am- 

 monites which are agatized, I found that the exterior shell was very 

 frequently distinguishable from the infiltered agate by being more 



