On South- American Geology. 565 



4. " On the Occurrence of a Remarkable and apparently New 

 Mineral in the Rocks of Inverness-shire." By William Jolly, Esq., 

 F.R.S.E. &c, H.M. Inspector of Schools, and J. Macdon aid-Cameron, 

 Eel. Inst. Chem., E.C.S., &c. 



In this paper the authors refer to a blue mineral of a somewhat 

 remarkable character, which was specially noticed during an excur- 

 sion of the Inverness Field Club in September 1877. This excursion 

 was made to Englishton Moor and neighbourhood, distant west- 

 wards from Inverness about 5 miles, where the mineral occurs in 

 scattered blocks. It has since been noticed at Moniack Burn, 

 Reelig Glen, and South Clunes Earm, all in the same direction, but 

 distant from Inverness about 10 miles ; also near Dochfour House, 

 at the north end of Loch Ness, close by Dochgarroch Lock of the 

 Caledonian Canal. In colour and general appearance this mineral 

 resembles crocidolite ; but analyses point to its being more nearly 

 related to segirite, a member of the amphibole group, which has the 

 general formula Si 3(|E+R 3 ). 



The mean of several analyses shows it to have the composition 

 6Si0 2 ,Ee 2 3 ,2MgO. 



June 25, 1879.— Prof . P. Martin Duncan, M.B., E.R.S., Vice- 

 President, in the Chair. 



The following communications were read : — 



1. "On the Evidence that certain Species of Ichthyosaurus were 

 Viviparous." By Prof. H. G. Seeley, E.R.S., E.G.S. 



2. " On BhampJiocephalus Prestwichi, Seeley, an Ornithosaurian 

 from the Stonesfield Slate of Kineton." By Prof. H. G. Seeley, 

 F.R.S., E.G.S. 



3. "A Contribution to South- American Geology." By George 

 Attwood, Esq., E.G.S. 



The paper describes a line of country in Spanish Guayana, Vene- 

 zuela, S. A., commencing from a small town called " the Port of 

 Las Tablas," on the Orinoco river, extending about 150 miles, 

 and consisting of a series of crystalline and altered rocks. Syenite 

 is the first rock met with ; and then are found granite, quartz-diorite, 

 haematite, and magnetic iron- ores, gneiss, slaty rocks, gabbro, and 

 diabase. 



In the diabase the quartz-veins are found to contain large 

 quantities of gold mixed with the vein-matter ; the alluvial soil 

 in the neighbourhood of the quartz-veins also contains gold nuggets 

 and small grains of gold. Although quartz-veins are found in 

 great numbers from the river to the interior, none of them has so 

 far been found to contain gold in any appreciable quantity until the 

 diabase is met with. 



All the rocks analyzed show a higher percentage of silica than is 

 generally found in other localities. Three analyses, made from one 

 piece of diabase showing two distinct lines of alteration by 

 weathering (on the original rock), prove that silica is readily dis- 

 eolved under atmospheric influences, whilst alumina is not. Iron 



