Amounts of progress upon this section of the work during present and preceding year are exhibited in the following comparative table:— ========================================================== West Shaft | Heading and Adit. | Enlargement. Section. +----------+--------+----------+------- | Linear | Cubic | Linear | Cubic | Feet. | Yards. | Feet. | Yards. -------------------+----------+--------+----------+------- YEAR ENDING | | | | November 1, 1867 | 543 | 2349 | 161 | 2100 November 1, 1868 | 1280 | 4696 | 82 | 488 ========================================================== The limited employment of Nitro-Glycerin made previous to August 1st, had been directed to excavations of enlargement, which very nearly resemble open cut work. The experience of the two months, August and September, is all we have that throws direct light upon its value in mining operations, using this phrase in its more limited sense, as applied to advance of heading only. The varying hardness and tenacity of rock and other attendant conditions, make material variations in the progress of separate days or weeks, even in the same drift and with the same means and appliances of working. For the reasons thus stated, actual records of advance without full knowledge and discussion of all attendant circumstances, and more especially when confined to short periods, must not be held conclusive in regard to the measure of advantage to be derived from its use. We cannot claim that in this short time, full knowledge as to its best possible application has been obtained. Its superiority over the powder ordinarily used in blasting, as demonstrated by our experience may be briefly expressed in the following items: “1. Less number of holes drilled in proportion to area of face carried forward. Estimated saving 33 per cent. “2. Greater depth of holes permissable. Average depth of Nitro-Glycerin, 42 inches; for blasting powder, 30 inches. “3. More complete avail of the full depth of hole drilled. The greatly superior explosive power of the Nitro-Glycerin rarely fails to take out the rock to the full depth of the hole. Powder often comes short of this, and by reason of this loss of useful effect, a large percentage of additional drilling becomes necessary. “In all the foregoing comparison, I assume it to be understood that simultaneous blasting by electric battery is employed. The great economy of force secured thereby, whenever hard rock may be encountered, is admitted by all conversant with the matter, and since the early part of the Summer, I have continuously employed it in both the headings advancing into the mountain.