THE lEON-BEARING MEMBER. 251 



fill assistance an increase of temperature is in the solution of silica is shown 

 by the geyserite deposits so well described b}' Hao^ue.^ While it may thus 

 be possible that a part of the silica is a direct chemical precipitate, it is cer- 

 tain that life is sufficient alone to collect from sea waters silica in solution 

 and form extensive deposits. So far as we know, this was first shown of 

 the Trimming-ham chalks, the chert of which seems without question to be 

 the remains of life." Later it has been shown by Dr. G. J. Hinde that ex- 

 tensive deposits of chert in Ireland, England, Wales and Spitzbergen are 

 largely, and possibly wholly, accumulations of sponge spicules. The 

 deposits of Ireland are described,' as follows: 



Tliey ooiisist of uddnlar masses of irregular form, iiu-losed in lieds of hard, bluish 

 limestout's, and following the planes of bedding' much in the same waj' as the tiints 

 in the Upper Chalk; but, unlike the Hint.s, these nodular masses are not sharply 

 delimited from the limestones in which they are interbedded, but there is a gradual 

 passage from tiie chert to the limestone. 



More fre(|uently, however, the cheit exists in dclinite beds from 1 to 5 inches 

 (.025-.12in.) in thickness, which intervene at ii'regiilar intervals between lieds of 

 limestone. These beds sometimes occur also as well marked layers in tlie central 

 jiortions of beds of limestone. Both the nodular aggregations and the horizon- 

 tally bedded chert usually occur in the same series of rocks. The particular mode of 

 deposition probably depends on the extent to which the sponge remains (ot which it 

 will be shown the chert cou.sists) are present in the respective areas. 



It will ]«' seen that this description conforms in a remarkable manner 

 to the occurrence of chert and carbonate in the Penokee series. At Spitz- 

 bergen, Axels island, Yorkshire, and Noi'th Wales there are alternations of 

 chert and limestone, the pure cherty layers of which are here, however, 

 often quite a number of feet in thickness. The most remarkable occur- 

 rence is that of Spitzbergen and Axels island. The beds of chert}- material 



'Geological History of the Yellowstone National Park, liy Arnold Hague. Trans. Am. In.st. Min. 

 Eug.. vol. .\vi. 18S8, i)p. 78S-803. 



-On the Flint Nodules of the Trinmiinghani Chalks. Iiy Prof. W. .1. Snilas. Annals Nat. Hist. 

 1880, i>v). S84 -Am. 437-461. 



'Ou the Organic Origin of the Chert in the ('arlioiiilerims I.inii'stone Series of Ireland, and its 

 similarity to that in the eorreB))onding strata in North Wales and Yorkshire, hy tieorge .Jennings Hinde. 

 Geo!. Mag., Loudon, New Series (Decade III), v<d. iv, jip. 435-44(>. On the Chert and .Siliceous Schists 

 of the Permo-Carhoniferous Strat.'i of Spitzbergen, and on the characters of the sponges therefrom, 

 which have been described by Dr. E. von Dunikowski. Dr. Hinde. Ibid., vol. v, pp.241, 251. 



