506 Notices of Memoirs — A. J. Sack — On Cone-in-Cone. 



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 con- 

 viction that the structure is one of the peculiar form of concretions 

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

 crystallization of the calcium carbonate and other isomorphous bases. 



Dr. Dawson, in his Acadian Geology, 18G8, 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. 



K. 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.G.S., Transactions of the Geological Society of 

 Glasgow, vol. viii., 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-Cone 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 esscape of gases generated by the decomposition 

 of organic matter in the deposit; the gases, as they escaped through 

 the oozy and plastic mud, elevated the sediment around the several 

 points of eruption into ring-like layers. 



The sample which I now exhibit occurs at Picton, New South 

 Wales, in the upper course of the Picton Creek, which traverses 

 a valley locally known as Glenforsa. The hills on either side are 

 well-grassed slopes of Wianamatta shales, which are of Triassic age, 

 and are generally considered of fresh-water origin. I do not know 

 of any extensive shell-beds or other lime deposit found in the shales, 

 but when traversing the glen some irregular nodules of calcium 

 carbonate were picked out of the banks of the creek. The Cone-in- 

 Cone mineral occurs as a horizontal layer, which is exposed in the 

 bed of the creek, but passes under the adjoining bank. So far as 

 I could learn, it is not now in process of formation. The thickness 

 is about two inches, composed entirely of cones within cones closely 

 packed together. It has been asserted that in some European 

 specimens the apices of the cones point both upward and downward, 

 l)ut m the specimen now under consideration all the apices point down- 

 ward. The open bases of the cones, formed of ampitheatre-like cavities, 

 are about half an inch in diameter, and small ones are sometimes 

 formed within the larger ones. The chemical composition of the 

 specimen is, approximately — Calcium carbonate, 67 54 per cent. ; 

 matter insoluble in strong hydrochloric acid, 21-2; sesquioxide of 

 iron, 4-14:; magnesium carbonate, 0'7 ; water, y-1. lu some parts 



