Originally charged No. 1 large bags,* 832. Used in reloading, The quantity of powder used per running linear foot varies according to the nature of the ground; but it is always large, because the slates, etc., are attacked edgeways. The average for six months amounts to: แ แ No. 1 Hercules powder per linear foot, 5.6 lbs. to 8.3 lbs. 66 connecting wire 2 1 ounces to 3.3 ounces per linear foot. "1.70 to 1.95 lbs. per linear foot. "steel I add the different distances to which the tunnel was driven at different dates. * A large bag weighs about 15 ounces; a small bag weighs about 8 5 ounces. I also add some of my results with the diamond drill, as it may be of interest to some of the members. I beg to state that I am convinced that the cost of diamonds would have been less, and the bore-holes would have been drilled in less time and at less expense, if I had had a proper supply of diamonds on hand from which to select. I also wish to note a fact which I have not read elsewhere, namely, in ground highly charged with iron pyrites the diamonds generally crumbled. It seems as if it disintegrated them to some extent. Having given a general description of the latest underground work, I wish now to say a few additional words with regard to the surface surroundings. A glance at the general map of the estate, which I copied in its outlines from a map of Max Strobel (see Fig. 5) shows the occurring veins all to have one general course, that is, northwest to southeast. The main croppings appear to be one continuous lode, from the Pine Tree and Josephine, where the vein is split into two, to Bear Valley and past it, along the slope of the Bullion Ridge to Mount Ophir and Princeton, and again in a split condition further on. They run sometimes apparently converging and then again diverging. East of Princeton are the Mariposa vein outcrops, and west of Bear Valley is the Oso vein with its croppings. The whole appears as a net of quartz veins, with the main axis running northwest and southeast. Referring to the map, we see Mount Bullion and its ridges form the northeast boundary, commencing on the Merced River. The country rocks have a similar trend to the outcrops, with a general dip to the northeast. Referring to the special map of the surroundings of the river tunnel (Plate I, Fig. 6), we notice on the northeast a heavy belt of serpentine, which rises with Mount Bullion. Exposed at intermediate points up the hill, back of the Josephine, it shows again boldly at Mount Ophir, and further southeast between Agua Fria and Mariposa. Skirting this northeast serpentine belt, as well on the east as on the west, we see the welldefined clay slates with their thin edges marked out sharply, and on the west side the dark blue slates. This belt of slates incloses the quartz veins and its general trend follows the axis of the valley all through the estate. Although in general the quartz veins correspond to the general trend of the slates, in detail they are not always conformable with them, as is especially well defined near and around the Princeton vein, where, as Prof. Blake already pointed out in 1864, this vein occupies the line of break between two distinct bodies of slate, the Diamond Bores made on the Mariposa Estate during the Summer of 1877. time lost. • Drill entered broken ground and stuck; was finally, after straightening out several hooks and breaking two blocks and three falls, extracted with a hydraulic jack, which accounts for the Had to ream on account of an insufficient supply of diamonds to keep up the gauge of the bit. 158 THE LATE OPERATIONS ON THE MARIPOSA ESTATE. eastern ones varying in trend from N. 45° to 90° W. Prof. Blake, who examined especially the middle portion of the estate, including Princeton Mine, made a very interesting cross sectional examination of the country in a general northeast and southwest direction. I add it, as it is of general interest. The southwestern end is taken along Bear Creek, the middle portion across the Princeton vein, and the remainder along a line nearly over upper Agua Fria, northeastward to Mount Bullion range. The following formations are represented : Coarse heavy conglomerates, metamorphosed. Slaty conglomerate. Argillaceous slates, regularly stratified (thick series). Sandstones and sandy beds (thin). Princeton gold vein. Argillaceous slate and quartz veins. Magnesian rock and quartz vein. Slaty conglomerate. Greenstone, limited in extent, probably a metamorphic sandstone. Sandy slates and sandstones. Serpentine and magnesian rocks (the northern extension of Buckeye ridge). Compact slates, crystalline and much changed in places by metal morphism. Bullion Range, metamorphic sandstone and heavy conglomerate, the so-called "Greenstone." This may suffice for a general outline of the geology of the estate, and I now recur to the northern portion, the River Tunnel. In the special map of the River Tunnel's surroundings, I have made use of the original tunnel line, which has been laid out by Mr. Thomas, county surveyor, and taking this as a basis and assuming it to be correct, I have connected with this and laid down the underground exposed quartz as determined by my own survey, as also the different and reticulated quartz croppings of the surface. I do not claim absolute correctness for the mountain roads as put in, for portions of them are filled in by guesswork, as I did not have time to finish my topographical survey owing to the stoppage in the work of the estate by foreclosure of the Kelly and Donohue mortgage. A question which arises is: Which croppings correspond to the vein which the tunnel has laid open? I cannot speak with absolute certainty owing to the premature closing of my survey, but I will say that two opinions are generally advanced: the one is, that the vein crops out |