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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



[Nov. 21, 



grey felspar-like mineral in it ; in texture it then much resem- 

 bles a basaltic or trappean rock. It is extremely hard and tough, 

 and is cracked, fissured, and jointed in all directions. Occasionally 

 one set of joints presents pretty regular and parallel lines of fracture. 

 Many small strings of copper-ores (sulphurets, carbonates, and oxy- 

 chlorides) are seen cutting through them, with various bearings, from 

 N.E. to E. and W., dipping at very high angles. 



Conclusion. — In conclusion, I must direct attention to the three 

 comparative sections of the country from Arica on the Pacific to the 

 Yungas on the eastern side of the High Andes of Bolivia (Plate III.). 

 Although this plate is, of course, to be regarded only as a diagram, it 

 represents correctly a summary of the conclusions at which M. D'Or- 

 bigny*, M. Pissisf, and myself have arrived in traversing the same 

 line of country. 



On examination, it will be observed that great and unaccountable 

 differences are here depicted ; and it must be left to the reader to 

 judge, from the perusal of the different memoirs of the three authors, 

 how far each of them may be sound in his views. 



This plate does not require any further explanation than the 

 remarks which have been occasionally made under the heads of the 

 different formations ; but it is particularly important as showing at a 

 glance these several discrepancies, and in its bearings on the general 

 tenor of the results here brought forward. Subsequently it will be 

 required for reference in the second and third parts of the memoir of 

 which this communication is the first part, and which will treat of 

 the Geology of Chile and the Argentine Provinces ; it will then be 

 found most essential in explaining and reconciling the various state- 

 ments which have been made in reference to the geology of these 

 countries. 



2. On the Fossils, from the High Aioes, collected by David Forbes, 

 Esq., F.R.S., F.G.S. By J. W. Salter, Esq., F.G.S. 



[Plates IV. & V.] 



I have examined this unique series with some care ; and with a col- 

 lection of above 200 specimens there should be no unusual difficulty 

 in assigning the true geological date. The specimens are generally 

 perfect enough to show the generic characters, though in very few 

 cases is their preservation complete ; and it is thought better at pre- 

 sent (especially as Mr. Forbes intends returning over this difficult 

 ground) to figure all the chief forms, and give specific characters 

 only to the more prominent fossils. All the specimens from the 

 slate-rocks are distinct from those previously published. 



* Voyage dans l'Amerique Meridionale, tome iii., Partie Geologic Par M. 

 Alcide d'Orbigny. Paris, 1842. 



t " Reeherches siir les Systeines de Soulevement de l'Amerique du Sud." Par 

 M. Pissis. Annales des Mines, 5 me ser. tome ix. 1856. 



