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THE BRITISH NATURALIST. 



37 



crossing the limestone ridge, proceed for a short distance at right angles 

 to the river, when we arrive at what looks like a small quarry. On 

 examining the face of the rock we shall find that the atmosphere has in 

 a decidedly marked manner affected its surface, moulding it into masses 

 of numerous round bosses, some smaller than an egg, others as large 

 as a football. If we pick up one of these " spheroids," as geologists call 

 them, many of which are lying at the foot of the rock, we shall find, on 

 inspection, that it is composed of a loose friable material, becoming 

 harder and more caked towards the centre, very different from the hard 

 metallic looking basalt or toadstone ! And yet not so different after all ! 

 For until those irresistible agents of denudation, the rain and the wind, 

 commenced their disintegrating action on the rock, the two substances 

 were practically identical, and w r ere we to penetrate far enough, we 

 should at length reach a portion of the rock analogous to the igneous 

 basalt in the limestone. 



Another important geological feature connected with the dale is the 

 occurrence of mineral veins or lodes, a good example of which is to be 

 met with down the right bank of the river, a short distance below Miller's 

 Dale station. The veins are formed by a deposit of mineral in a crack 

 or joint of the rock, which may have been enlarged by a stream of water 

 containing carbonic acid in solution. 



In this vein the limestone has been divided by a layer of toadstone 

 cutting the lode at right angles, where it has become extremely narrow, 

 owing to the smailness of the crack in the toadstone, on which the water 

 has acted comparatively slowly. Crossing the river, the vein still 

 continues to traverse the limestone cracks, where it has not been worked, 

 and further on it practically terminates at a " fault " : a place where a 

 portion of the limestone bed has been broken off and forced into a 

 different plane from that of the original bed. The fact is obvious enough 

 from the similarity of the two surfaces, there being just a trace of the 

 " rake-vein " in the newly located limestone corresponding to the lode in 

 the old bed. 



A "rake-vein" is a vein which traverser the strata vertically, or 

 nearly so, and averages the same thickness throughout its length. Part 

 of this "rake " has been worked for lead, and near the mouth is a large 

 heap of excavated residue, which will well repay a cursory examination. 

 Breaking up a piece with our hammer, we find it composed of a white 

 semi-crystalline mass, dotted here and there with flat shining black 

 crystals. They are what is known as galena, or sulphide of lead, and 

 probably may contain traces of silver, the two metals generally going 

 together ; the white crystals are carbonate of calcium or calcite. 

 Another piece shows white crystals of lead carbonate, and another of 

 purplish colour is felspar, a compound of silica, alumina, and potash. 

 There are many other interesting compounds to be found, and a great 



