362 



THE GEOLOGIST. 



tlirougli them. These veins are seldom highly inclined as regards 

 the relationship of their plane to the vertical plane of the rocks ; and 

 considered with regard to their contents, only become productive in 

 the immediate vicinity of, or at their conjuncture with, the pipe 

 veins. It is, indeed, questionable whether they may exist even as 

 fissures at any very great distance from the pipes ; at any rate, their 

 origin may be safely assumed as contemporaneous. They are not 

 often twitched, or, in other words, the spaces between the walls 

 seldom present any great irregularities of size, such as commonly 

 arise where the edges of the strata, originally opposite, by the nature 

 of the fault are brought to different levels. The direction of the 

 rake veins varies, but a great number have been observed to run 

 north-north-west to north-west. Crossing them, usually at nearly 

 right angles, are other similar veins, which however must not be 

 confounded with another set of great fractures which extend east and 

 west, or nearly so, through a considerable extent of the country, and 

 frequently intersect the saddle-beds in the direction of their strike. 

 These fissures are locally known as " lums," this name having an analo- 

 gous signification in raining language with what are elsewhere called 

 cross-courses, although they differ essentially from these both in 

 their mineral contents as well as in their effects on the veins with 

 which they are associated and cut across. 



The lignograph, fig. 3, represents an ideal block, or parallelepiped, 

 of the country in the neighbourhood of the Ecton and Dale mines 

 without reference to the surface, and exhibits the strata, 1st, as they 

 would be seen in vertical section on their line of strike ; and 2nd, as 

 they would be seen in vertical section in the direction of their dip. 

 The plane A B E F shows the contorted beds, or saddles, and those 

 which are superincumbent but not contorted, h c d e : A B E F is 

 also the plane of the cross-course, called the lum, which consequently 

 intersects the saddles vertically. The general featm'es of the pipe- 

 vein E F' in this diagram have been already explained, but F g, 

 F g', F g" will show the connectionship of this vein and the rake- 

 veins, as seen in plan ; the bearing of the rake-veins is north-east, 

 south-west, and south-east. The gradual dying out of the con- 

 tortions towards their crop at the surface, where they form, as 

 already stated, merely waved strata, a' a', explains itself by the 

 dotted lines x ij z. The dotted line o is supposed to proceed from 

 saddle-beds much lower in the series (see also p. 365J, and which 

 consequently crop out a great deal farther to the south. 



When considering the origin of metalliferous accumulations 

 whether in igneous or stratified formations, any peculiarities in the 

 composition of the rocks are as important to notice as are differences 

 of structure in the same rocks. It may be, therefore, here mentioned 

 that many of the beds in the vicinit}^ of the saddles, at Ecton and 

 clst>\vliev(\ are highly charged with silica — either in a segregated 

 form as pseudo-strata intercalated between the coursings of the 

 stone, or by a species of pseudo-morphism : a bed of limestone, while 

 retaining m^nj of the mai-ks of its sedimentary origin, is wholly, or 



