Vol. 5] 



Louderback. — 



Benitoite 



339 



fiver the natrolite, and disfigured its shining pure white surface. 

 The general dark areas in plate 29 are due to limonite films. 

 Fortunately, the benitoite and most of its associates are very 

 resistant to weathering, and besides they are generally well en- 

 closed in impregnated blocks that shed the water into their more 

 porous neighbors. Plate 32 is a more general view of the face 

 of the cut, and the distribution of vein-stone can be there 

 better followed. The rope lies on the fault-plane, and to 

 its right is the sheeted greenstone. Starting from the curve in 

 the rope, to the left a number of harder block's arc to be seen 

 lying almost on a level. These are all "ore". Above them is 

 a greenish blue, porous, highly altered country, characterized 

 by an extensive development of green to blue amphiboles. At 

 the left edge of the photograph is a large mass extending to 

 the floor of the cut. It is evidently a breccia, and is highly 

 impregnated. It also is "ore", if in part low grade. This mass 

 extended out originally into the cut, where it was separated 

 from the vein-stone in the face as a result of a transverse fault. 

 The zone here dips to the left. Its irregularity is evident. The 

 highest visible point of the rim is thirty-seven feet above the 

 floor of the cut. 



AYe may consider briefly the practical bearings of these post- 

 veination movements. They have increased the difficulty of 

 mining by producing irregularity and discontinuity of the gem- 

 bearing matrix, by leaving the rock in a weakened condition so 

 that movement and caving are always imminent, and by afford- 

 ing ready access of surface water into the workings. 



The workings are at present so shallow that there is not suf- 

 ficient evidence on which to base an opinion as to whether these 

 conditions will change or not with increasing depth. 



SIZE AND ATTITUDE OF OUTCROP. 



The outcrop of the mineralized zone is not very extensive. 

 At its widest point it is about sixty-four feet. Its length is not 

 over four hundred feet. Of this the easternmost part carries 

 barren natrolite veinlets and the wall-rock shows a minimum 

 of metasomatic alteration. Benitoite has been found at the sur- 

 face along only about 230 feet of the zone, and at Hie extremes 

 of this distance only in very small quantity. 



