486 



T. C. HOl'KINS — CAMBROSILURIAN U.MoXITE ORES 



tlie argillaceous and silicious matter in the Beam, and not in direct con- 

 tact with the limestone, which is a sandy, silicious variety. Leaving on 

 the weathered surface, in places, a silicious skeleton or framework some- 

 times coated with ore. The ore is laminated parallel with the walls of 



the seams. As the limestone decays, the thin sheets of ore break down 

 and mingle with the residual clay, furnishing the commercial ores. The 

 ore which occurs in place in the seams in the limestone and the frag- 

 ments visible in the residual clay are all thin and fragile so far as ob- 

 served ; but the bottoms of the ore pockets are concealed by debris, and 

 it is possible that the sheets become thicker at greater depths, as is 

 frequently reported by the workmen. 



In the slate areas the ore with the other residua rests upon a mass of 

 clay, in many cases white clay, stained locally by iron oxides. As the 

 slates from which the clays are derived are inters tratified with the lime- 

 stones, there can be no very sharp distinction drawn between the ore 



deposits on the limestone 

 and those on the clay. In 

 many districts the greater 

 part of the ore deposits are 

 found on the white clay. 

 So common is this occur- 

 rence that it may be stated 



Figure 3. — Ideal Section Illustrating Possible Modt of Accum- <\S a general rule that ill 

 ulatinq Iron Ore underneath tin Clay by Process of Seqreaation -, ,1 t 



and Leaching. areaS where the cla ~ VS 0CCUr 



they are associated with the 

 ore deposits, but where the clays are absent the ores occur in the eroded 

 cavities in the limestone, as described above. One general distinction 

 can be made between the purely limestone deposits and the limestone- 

 clay deposits. The latter are generally richer at the bottom in direct 

 contact with the white clay, while the former may be as rich at the top 

 as at the bottom. Solid bodies of ore are spoken of by the miners in 

 many places, but I have never seen any such more than a few hundred 

 pounds in weight that were not mixed with foreign materials. Professor 

 Prime, who examined many of the Lehigh Valley mines when the} 7 " were 

 in operation, says:* "At times a thick, solid bank of ore is found in a 

 mine. This is, however, rare, and continues but a short distance." 

 Lesley t mentions the occurrence of such bodies, but his statements 

 appear to be based on reports by mine superintendents, rather than on 

 his own observations. 



Occasionally ore bodies are found in or underneath the white clay. 



* Second Geol. Survey of Pennsylvania, Reporl 1> 1», p. 50 

 fProc, Am, Phil, ><>(■., vol. xiv, 



