2 



J. A. PHILLIPS ON TELE OCCURRENCE OF REMAINS 



Government and by various private speculators until 1873, when 

 they were purchased by an English company. The extent of the 

 mining and metallurgical operations anciently carried on in this 

 district will be understood when it is stated that at Bio Tinto alone, 

 in addition to hundreds of Roman shafts and miles of Roman 

 galleries, the heaps of copper slags resulting from the smelting at 

 that period cannot amount to much less than one and a half million 

 of tons, and that there are large accumulations of similar ancient 

 refuse at Tharsis, Buitron, and other mines. 



As illustrating the care and skill of the metallurgists of that period 

 it may be stated that each ton of their slags seldom contains above 

 three pounds of copper. 



The prevailing rock throughout this region is clay-slate, which, 

 from the evidence of various fossils found by Mr. A. Hill, Mr. 

 G. "W. Clement, and other officers on the staff at Bio Tinto, is 

 apparently of Silurian age. These specimens were kindly examined 

 by Mr. R. Etheridge, who did not hesitate to identify them as 

 belonging to that period. 



These slates are, in places, broken through by large dykes of 

 quartz-porphyry, which frequently form one of the walls of the 

 various deposits of cupreous pyrites. 



The fossiliferous iron-ore which is the immediate subject of this 

 note forms a cap one kilometre long, with an average width of one 

 hundred and thirty metres, on the top of the Mesa de los Pinos, 

 nine hundred metres south of the open cutting at Bio Tinto. Its 

 surface is approximately level, but it varies in depth from one to 

 seventeen metres in accordance with the conformation of the surface 

 of the slate upon which it lies ; the rock beneath it is bleached and 

 to some extent decomposed. 



The order and relative positions of the several formations will be 

 best understood on referring to the accompanying plan and section 

 (figs. 1, 2), for which I am indebted to Mr. Weil Kennedy, a gentle- 

 man in charge of a portion of the work at the mines, through whose 

 kindness I am also enabled to lay specimens of the fossiliferous iron- 

 ore upon the table. 



On the extreme right of the section is a broad porphyritic dyke 

 forming the north wall of the south lode, next to which is the lode 

 itself, which at this point has only one third of its greatest width* 

 Next in succession, to the south, comes a band of slate, which 

 is again penetrated on the left by a broad dyke of quartz-porphyry. 

 It will be observed that the upper part of the vein has, to a con- 

 siderable depth, been converted into a ferruginous capping (gossan), 

 of which a large portion has been removed by denudation. The 

 stratum of iron-ore forming the surface at the Mesa de los Pinos 

 is shown with precipitous sides ; and a small patch of a similar- 

 formation occurs, at within a metre of the same elevation, at the 

 Cerro de las Yacas. Numerous fissures occur in the surface of the x 

 larger deposit of iron-ore, and out of these pine-trees formerly 

 grew in considerable numbers, their presence giving the name to 

 the locality ; these were eventually destroyed by sulphurous fumes 



