14 



TAB, cecx. 



S 1 L E X Q u artzu m , -oar 



Sh ell-formed Ca Ice do ny . 



Biv. 2. Imitative. Far. Shell-like, 



I AM obliged to the generosity of Mr. Milne of Foothill 

 for this specimen. That place and the neighbourhood often 

 afford Cornua Ammonis of very extraordinary dimensions. 

 I was told of one that was at Tisbury nearly as big as the 

 large wheel of a coach. I have one of 21 inches in diameter, 

 and my friend Mr. W. Cunnington has one larger. They 

 are often of Sandy Limestone, or Limestone with crystals 

 within, and now and then there are found the remains of 

 similar shells in Flint with the chambered divisions partly 

 calcedonized, if I may use the expression, and containing 

 Quartz crystals; but the most curious specimen ever seen 

 is the present, except one as nearly like it as possible, 

 which I am told is in the possession of Sir Edward Halse 

 of Salisbury. It is perhaps as extraordinary a geological 

 specimen as any that have been seen. The mass is 

 chiefly Flint; but the shell has been lined, and having sub- 

 sequently decayed, left the Calcedony of the. most delicate 

 and exquisite structure. The peculiarly regular folding 

 manner of the divisions, and their uniformity, are no where 

 disturbed. The Calcedony is placed distinctly around 

 where the shell originally was. There are other minute 

 shells about the specimen, and^ also some Carbonate of 

 Lime, both crystallized and amorphous. 



The lower jigure exhibits one of the partitions, showing 

 the tube which passes round the shell, different from what 

 is usual, as not being a continued channel, but divided into 

 short tubes, each of which communicates by its openings 

 with two chambers. 



Geologists, as they contemplate the changes which have 

 here taken place, may well join with David, Linneus, and 

 all true philosophers, in exclaiming, (i Oh ! Jehovah, 

 great and manifold are thy works ; in wisdom hast thou 

 made them all ; the Earth is full of thy riches." 



Sir H. C. Encrlefield showed me a beautiful specimen of a 

 spiral shell with the end passing from Calcedony to Opak 



