TRANSACTIONS OF THE SECTIONS. 79 



On some Transformations of Iron Pyrites in connexion with Organic Remains. 



By Alphonse Gages. 



I have to direct the attention of the Section to some facts regarding the transforma- 

 tion of iron pyrites connected with fossil graptolites from Tinnaglough, Co. Wexford. 



These peculiar characteristic fossils of the Lower Silurian schists are found very 

 often transformed into rhombic iron pyrites. 



This transformation into pyrites is now, since the observations of Pepys and others, 

 easily accounted for, and therefore I have not to dwell upon it. 



Looking over some of those schists, we may observe the various transformations 

 the fossil has passed through until it entirely disappears from the schist. 



I. Fossil exhibiting some traces of organic matter, and not mineralized by pyrites. 



II. The same fossil transformed into rhombic iron pyrites. 



III. The transformation of the pyritic fossil into a corresponding fossil of aluminite. 



IV. A mere cast of the fossil, or indication of one only remaining. 



And lastly, in some neighbouring joints of the schist, a thin layer of sesquioxide of 

 iron, alum, or of aluminite generally accompanied by free sulphur. 



Analogous phenomena may be observed in other fossils of the carboniferous form- 

 ation, and especially in the lower limestone shale near Drogheda. 



One may observe in some points in which the fossil has been completely obliterated, 

 a thin mineral layer of aluminous compounds, varying more or less in their chemical 

 constitution. 



These facts are very suggestive in this sense, that if the processes of mineralization 

 going on for ages have served to preserve many forms of organic beings, so also they 

 serve to destroy them. 



We witness every day the destruction of a great number of pyritic fossils by the 

 mere action of air, and their transformation into sulphates, and sometimes, according 

 to local circumstances, into sulphates and free sulphur. Whenever sulphur occurs 

 in deposits containing organic remains, we are induced to believe that it has been 

 formed in somewhat a similar way. 



On Snow Crystals observed at Dresden. By Dr. Geinitz. 



On the Silurian Formation in the District of Wilsdruff. By Dr. Geinitz. 



The discovery of Graptolites in the Lydit and Phthanit, lately made in the district 

 of Wilsdruff, near the villages of Limbach, Lotzen, and Lampersdorf, a neighbour- 

 hood where the azoic and metamorphic clay-slates, sometimes with true chiastolith, 

 are predominant, now combines a considerable part of the most northern part of the 

 Saxon Erzgebirge with the Silurian. 



These black schists of Graptolites, with Monograpsus triangulatus, Harkness, Mon. 

 priodon, Bronn, Mon. Becki, Barrande, and Mon. nuntius, Barrande, are continued in 

 the schists of Graptolites on the northern slope of the Erzgebirge near Langenstriegis, 

 not far from Frankenberg, Ober-Cainsdorf near Zwickau, Ronneburg, Oelsnitz, Hein- 

 richsruhe near Schleiz, and various places of the district called Voigtland, where they 

 indicate the same geological horizon as in Bohemia, the upper part of the Lower 

 Silurian, or the base of the Upper Silurian of M. Barrande. All the species found 

 in Saxony are described in the author's 'Monograph of Graptolites,' Leipzig, 1852. 



On the Metamorphic Rochs of the North of Ireland. By Robert Hark- 

 ness, F.R.S., F.G.S., Professor of Geology in Queens College, Cork. 



Almost the whole of the county of Donegal is occupied by rocks which appertain 

 to the metamorphic series, consisting of gneissose rocks associated with limestones 

 and quartz rocks. The relation which these several rocks bear to each other, and to 

 the syenitic masses which in some cases are found accompanying them, is well exhi- 

 bited in the sections along the north side of Lough Foyle, from Malin Head to Inis- 

 howen Head. On the S.W. side of Malin Head a protrusion of syenite is seen, which 

 forms an axis in this portion of Ireland ; and reposing on this axis there are found, 

 first and lowest, quartz-rocks, succeeded conformably, on the north side, by flaggy 

 gneiss ; and on the southern side a like occurrence commonly takes place. In some 



