WATSON— NOTES ON METxVLLIFEROUS SADDLES. 



361 



might have been, continued to act from the right on the lower por- 

 tion of the already contorted beds. 



In the shale beds these rapid contortions do not strike ns with so 

 much surprise as when the phenomena is seen in the more massive 

 and coherent beds of limestone ; and then it seems scarcely credible, 

 even to the geologist, that the folded strata could ever have been de- 

 posited horizontally, and that, with comparatively so little fracture, 

 they could have been bent into their present form by simple pressu.re. 

 In cases where a separate well marked bed, left standing, forms the 

 roof and sides of a level in a mine, the entrance to such level from a 

 transverse gallery or shaft wears all the appearance of an arch of 

 artificial masonry, and the deception is only removed by close 

 inspection of the contiguous rock. Natural arches, formed by the 

 weathering and removal of the soft beds, are not uncommon in cliff 

 sections of contorted rocks, but then the spread of the strata is 

 usually much wider, and the idea of such vast compressing force 

 having been put in action is not so obtruding. The coal-measure 

 " binds" (argillaceous sandstones) on the shores of Carmarthen Bay 

 between Saundersfoot and Tenby display some very remarkable ex- 

 amples of weathered contorted beds, but they are in no respects 

 equally striking with those of the limestone strata above described. 



l^ext to the form, and structure of the saddles we may conveniently 

 consider the associated minerals ; but, before we can do this satis- 

 factorily, the circumstances connected with their union with the 

 metallic veins — which invariably, in the districts which now occupy 

 us, form part of the general system of displacements of the stratifica- 

 tion — must have our attention ; and perhaps it may simplify matters 

 in this respect if we select an example for description. Let us take 

 the case of the Old Ecton mine, in the parish of Alstonfields, North 

 Stafiord shire. This mine deserves our choice not only because it has 

 made very large returns of ore, but also because, from the length of 

 time it has been working, the ground has been so thoroughly opened 

 that the relationship between the saddles and veins has been better 

 made out than in more recently opened and less developed setts in 

 that neighbourhood. The veins which here exist are " pipe veins" 

 and "rake veins," and may be thus particularized. 



The pipe veins are irregular cavities inclined at angles varying from 

 fifteen to thirty-five degrees to the horizon; have no proper longitu- 

 dinal bearing, like the Cornish lodes for instance ; and have generally 

 the most important of their expansions parallel to the bedding of the 

 strata which they traverse ; and v/hose dip is also the direction of 

 the pipes, although these are by no means always confined to any 

 distinct bed of stone, but, on the contrary, usually pass through 

 several beds in succession until they reach the saddles. The general 

 relations of a pipe vein to the stratification of the rocks is shown in 

 fig. "d, E B, which also represents the course of such a vein through 

 the different beds in the direction of their dip, as just mentioned. 



The rake veins in the Ecton district are usually a series of verticpJ 

 fissures falling in with the pipe veins, and, occasionally, passing 

 VOL. III. 2 z 



