STRUCTURE OF RUBY HILL. 37 



Lower shale in the Eureka. — This underground shale is exposed in the cross-cut 

 from the twelfth level of the Eureka mine to the Locan shaft. Vertical 

 cross-section No 7, Plate VIII., shows the position of this shale. At this 

 point it is very narrow, not exceeding 20 feet, and is more or less mixed 

 with stratified limestone. In this region it probably extends up as high as 

 the little tenth, and it forms the hanging wall of the main fissure, which 

 takes up the space between it and the quartzite. During the process ot 

 upheaval which formed the main fissure and the secondary fissure at the con- 

 tact of the quartzite and limestone, there was considerable motion along 

 the face of the quartzite, and the shale which lay northeast of the fissure 

 was dragged upward, so that where it forms the hanging wall the dip of its 

 stratification is nearly parallel with that of the fissure. This can be noticed 

 in the cross-cut. The natural dip of the shale, however, is less than 40°, 

 so that as depth is attained it will gradually pitcli off flatter and the lime- 

 stone will again make its appearance in the form of a wedge between the 

 fissure and the shale. This occurrence is already indicated on the thir- 

 teenth and fourteenth levels, where the limestone appears to be growing 

 wider. This limestone, having been subjected to a pressure similar to that 

 exerted in the upper wedge between the hanging wall of the main fissure 

 and the quartzite, will be found to be in a like crushed and broken state. 

 At a point on the tenth level just over the main incline, 140 feet above the 

 twelfth, the shale is found in contact with the main fissure, which is here 

 some distance from the quartzite. In going southeast from this point the 

 shale gives out, but in going northwest it is found in contact with the fissure. 

 Further along toward the compromise line the cross-cut passes through it 

 for 120 feet before reaching the limestone. Above this point the shale 

 reaches as high as the little tenth, always forming the hanging wall of the 

 fissure, but was not found where the fissure has been cut above it on the 

 ninth. Below the twelfth level it was not possible to inspect it, as the thir- 

 teenth and fourteenth levels have been under water for several years, but 

 from information obtained it must occupy about the position laid down on 

 the map. 



This shale may or may not be the same as that which is found in the 

 Phoenix and Jackson, but the fact before mentioned, that it lies in a line 



