396 Scientific Intelligence. 



ten or fifteen feet in thickness, and within one hundred feet of 

 each other. The lowest sheet is characterized by the presence of 

 silver ores, to the exclusion of gold ; the middle sheet by gold 

 ores, with no silver ; while the uppermost sheet, which is espec- 

 ially thin and intermittent, is not mineralized to any extent. The 

 gold and silver horizon are known as the Gold and Silver Ledges 

 respectively. 



The Silver Ledge is marked by complete silification of the 

 limestone, and by barite in irregular masses, with some stibnite 

 and a little copper and silver. It is probable that the metals 

 were originally deposited as sulphides, and that they were intro- 

 duced into their present position, together with quartz and barite, 

 by ascending waters; and the phenomena accord best with the 

 idea that the mineralization was accomplished by waters excluded 

 from the porphyry during its consolidation, and that thus the ore- 

 deposit is a special case of contact-metamorphism. 



The Gold Ledge, which is situated about one hundred feet ver- 

 tically above the Silver Ledge, is characterized by a softened con- 

 dition of the ores, whether in the normal condition of sulphide, 

 or in the zone which has been bleached and altered by surface 

 oxidation. Its most characteristic feature is realgar, which occurs 

 in large amounts in the unoxidized ores, with frequent cinnabar 

 and gold in small, but in certain zones nearly uniform, quantities. 

 The gold is in extremely finely divided condition ; but it is prob- 

 able that it exists in the unaltered form as telluride, and that on 

 oxidation it has become free gold. Evidence shows that the 

 mineralization of the gold-horizon took place at a distinctly later 

 date than that of the silver-horizon ; and that the mineralizing 

 agents were probably in a vaporous rather than in a liquid form. 



2. Catalogue of the Fossil Fishes in the British Museum, 

 Part III, containing the Actinopterygian Teleostomi of the 

 orders Ghondrostei (concluded), Protospondyli, Aetheospondyli, 

 and Isospondyli (in part) ; by A. S. Woodward ; pp. 1-544, pis. 

 1-xviii. London, 1895. — Mr. Woodward's introduction, of about 

 twenty pages, is full of important conclusions, derived from his 

 exhaustive study of the Actinopterygian fishes, regarding the 

 phylogenetic relations of the several families. In the arrange- 

 ment of the material in the catalogue, the author has attempted 

 to record, in as nearly a natural order as possible, the variation of 

 each type at the time of its dominance. The origin of the 

 Chondrostei is obscure, but that they are later than the Crossop- 

 terygians is evident. When they first became dominant in the 

 lower Carboniferous they exhibited a remarkable sense of modifica- 

 tion and thereafter suffered very little essential change. The genus 

 Acentrophorus of the upper Permian is the first of the sub-order 

 Protospondyli, and it is observed to be the most generalized mem- 

 ber of the iamily to which it belongs (Semionolidaa) which is also 

 the most generalized family of its series. 



The same fact is noted regarding Ophiopsis, the most general- 

 ized genus of the family Macrosemeidse, and the earliest to ap- 

 pear. 



