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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Jan. 23, 



about thirty acres are crowded the whole of the " plant" and buildings 

 of two extensive mines, and part of a third, with dressing-floors and 

 ore-heaps on a scale rarely seen *, as it seldom happens that so much 

 ore has been raised from a single group of lodes of such small extent. 

 The diagram fig. 3 marks the limits of the concessions, and thus 

 shows the small extent of surface ; but it gives no idea of the crowding 

 that has necessarily resulted from the form of the ground, which 

 is extremely broken, and in many parts precipitous. The section 

 fig. 4 will, however, assist in giving an idea of these peculiarities. 



Fig. 4. — Section across the Mineral Field of Cobre. 

 (Length of Section about 1200 yards.) 



c. Conglomerate. p. Porphyry. 



A.B. Line of Section on the Map, fig. 3. 



Contents of the Lode. — The rich part of the lode is for the most 

 part contained in the precipitous hill on which the old and now 

 ruined church stands, and the ground here, at one time the source 

 of litigation amongst three companies, is now entirely undermined. 

 The enclosing "country," of which the shell of this hill is composed — 

 the contents consisting almost entirely of veinstone, formerly largely 

 mixed with red ore (of which nearly a million tons have been re- 

 moved), — is a confused mass of material scarcely distinguishable 

 from a coarse breccia of the adjacent porphyries, with the exception 

 of some more schistose portions, and of grits met with in descend- 

 ing. This material, identical with that which formed the hill now 

 fissured, has no doubt fallen into the cavity or rent formed by some 

 subterranean elevatory force. The whole group of lodes may 

 be described as a multitude of yawning cavities, connected with 

 innumerable smaller crevices, having, for the most part, an east and 

 west extension, but crossed by other crevices of the nature of small 

 faults or heaves, all more or less nearly at right angles, and termi- 

 nated towards the west by one such cross-course, beyond which no 

 ore has yet been found. 



Towards the east, the crevices or veins become gradually of less 

 importance, and pass into a vein containing but little valuable ore, 

 though clearly traceable for some distance at the surface. (See 

 map, fig. 3.) 



The whole outcrop of the great lode on this hill has been so much 



* At the time of my visit there were not less than 5000 tons of dressed ore 

 ready for shipment belonging to the Cobre mine alone. 



