328 PROCEEDINGS OF SECTION C, 



theory of my own that I exhibit the present specimen and 

 offer a few remarks on its composition and structure. 



Out of some half-dozen of geological text-books that I 

 consulted in the public libraries of Sydney, that by Archibald 

 Geikie, F.R.S., is the only one containing a reference to the 

 cone-in-cone structure. Geikie appears to adopt the opinion 

 of Professor Marsh, who states that the complex structure 

 known as cone-in-cone may be due to the action of pressure 

 upon concretions in the course of formation. 



H. C. Sorby, F.R.S., in a paper read before the British 

 Association, 1859, stated that he had examined transparent 

 sections of the structure with a low magnifying power under 

 polarized light, and concluded that it was intimately connected 

 with some kind of oolitic grains, which have crystals of 

 calcium carbonate deposited almost entirely on one side along 

 the axis of the cones in such a fan -shaped manner as to give 

 rise to their conical shape. He states his conviction that the 

 structure is one of the peculiar form of concretions formed 

 after the deposition of the rock in which they occur by the 

 crystallisation of the calcium carbonate and other isomorphous 

 bases. 



Dr. Dawson, in his Acadian Geology, 1868, asserts that 

 the structure is produced by concretionary action proceeding 

 from the surface of a bed or layer, and modified by gradual 

 compression of the material. 



R. Daintree, F.G.S., Quarterly Journal of Geological 

 Society, Vol. XXVIII., 1872, says that the structure has 

 more of the appearance of a chemical precipitate than of a 

 mechanical deposit. 



John Young, F.C.S.S., Transactions of the Geological 

 Society of Glasgow, Vol. \ III., read a paper on the subject 

 in 1885. He possessed evidence that the band of cone-in- 

 cone structure, which he described, rested on a clay-band 

 ironstone, and that it was on the same horizon as a bed of 

 stratified shale composed in bulk of calcareous shells of 

 entomostraca, of species frequenting lacustrine waters. He 

 possessed many samples of the mineral which had been found 

 in Scotland, and none had been associated with marine 

 deposits. After careful examination he concluded that the 

 cone-in-eone structure is the result of a mechanical action 

 set up by chemical agencies generated in the stratum, and 

 whilst the deposition of the sediment was going on. The 

 chemical agencies were the outward and upward escape of 

 gases generated by the decomposition of organic matter in 



