Beports and Froceedings — Geological Society of London. 181 



Ammonites of the Yorkshire Lias, in a short Monograph. Later on, 

 in 1855, he published descriptions of all the then known fossils of 

 this formation, together with an outline of the Geology of the York- 

 shire Coast, intended as a guide to strangers. In the fourth edition 

 of this " Guide " (published in 1868) he gave a section of the Lias, 

 carefully measured in detail, and noted the fossils which he had 

 collected from each stratum. This section is now reprinted, with 

 slight alterations, and the fossils, recorded in the work before us, are 

 referred to their particular horizons in the section. The estimates of 

 the thickness of the Lias differ from those given by Messrs. Tate 

 and Blake in their "Yorkshire Lias." The chief value of Mr. 

 Simpson's work, however, consists in his records of the positions in 

 which the fossils occur. His descriptions of the species, being un- 

 accompanied by figures, will not, we feai-, be of very great service to 

 collectors. 



s,e:pos,ts j^isiT^ ipi^ooiBEiDiiNros. 



I. — Geological Society of London. 

 {Continued from p. 137.) 



January 28, 1885.— Prof. T. G. Bonney, D.Sc, LL.D., F.E.S., 

 President, in the Chair. The following communications were read : 



2. " On the Geology of the Eio-Tinto Mines, with some general 

 remarks on the Pyritic Region of the Sierra Morena." By J. H. 

 Collins, Esq., F.G.S. 



After briefly describing the geographical position of the Eio-Tinto 

 mines, and the occurrence at the same of pyritous ores amongst 

 slates and schists which abut against gneissose rocks to the north, 

 and pass under Tertiary beds to the southward, the author pro- 

 ceeded to consider the general characters and associations of the 

 pyrites-deposits, and then gave a general account of the Eio-Tinto 

 district. The slates weie described, and the fossil evidence recapi- 

 tulated upon which an Upper Devonian age had been assigned to 

 them. Analyses were furnished to show the changes due to 

 weathering and to infiltration. The various intrusive rocks (syenite, 

 diabase, and porphyries) occurring in the schists were described, and 

 analyses of them given. The sedimentary iron-ores and their com- 

 position were next noticed, and the author ascribed their formation 

 to deposition in lakes. 



The masses of pyrites which furnish the principal ores of Eio 

 Tinto were then described, their mode of occurrence in fissures 

 between dissimilar rocks explained, and their formation discussed. 

 The diiferent kinds of ore obtained from the mines were noticed in 

 detail, and several analyses added, giving samples both of the mixed 

 ores and of the pure minerals. 



The manganese-lodes were next described, and shown to be 

 parallel to the pyrites-fissures, and frequently to be only branches of 

 the latter. 



A summary of the author's conclusions as to the stratigraphy of 

 the district, the ore-deposits, and the surface-geology was appended. 



