200 



over the surface of the rock will help to distinguish them at once. 

 I have long been accustomed, in field geology, to discriminate 

 between them by merely scraping the sole of an iron-shod boot 

 over the rock. The iron will slip easily enough over the rock 

 when it is dolomite, but it is rasped in a manner that is unmistake- 

 able when the rock under foot is sandstone. 



SiDERiTE, Chalybite, Spathose Iron, or White Iron Ore, the 

 Iron-Carbonate, is another generally-diffused mineral, though it 

 occurs in noticeable quantities only in a few localities. These are 

 chiefly in connection with the faults traversing the great upland 

 tract whose fell-tops form a great plain inclined from the line of 

 the Cross Fell escarpment in the direction of the Tyne Valley. 

 Here the ore occurs chiefly in the form of rider, or vein-stuff in 

 the fault-breccia ; but Professor Warington Smyth states that the 

 limestone adjoining the veins has itself been converted into 

 Siderite, which constitutes "flots," similar in their general character 

 to the lateral ramifications already referred to as one of the modes 

 of occurrence of Galena. The formation of Siderite has, however, 

 in this instance, clearly been due to the partial replacement 

 of the limestone in sitit, in a manner analagous to that referred to 

 under Dolomite. Indeed, it seems far from unlikely that Dolomite 

 may have formed a preliminary stage in the alteration ; and that 

 the formation of both minerals may be due to the influence of 

 solutions infiltring downwards through fault-fissures before the New 

 Red had been denuded from the old surface whose remains now 

 form the fell-tops there. In the part of the district now referred 

 to, Siderite occurs in quantities sufficient to constitute deposits of 

 some commercial importance. In other parts of the district it 

 rarely occurs in quantities that will pay for working. 



Siderite, in an impure form, mixed with earthy matter, occurs in 

 the form of nodular concretions, locally known as "cat heads," in 

 some of the shales of the Carboniferous series. These are occa- 

 sionally found in quantities sufficient to pay for working. In the 

 Argill Coal Field, described in Part VII. of the Transactions, 

 mention was made of some nodules of clay-ironstone that have 

 been converted superficially into haematite, by the partial replace- 



