The average duration of flat, wire ropes is usually taken at one year, and that of round ropes at half a year.

DIAMOND DRILLING.

This drill is applicable to sinking a borehole for prospecting for minerals or water, shafts, &c., or blasting under water.

It consists of a circular row of “carbonados,” a species of diamond, set in a circular steel ring. This is attached to a hollow steel tube which is kept rotating at about 250 revolutions per minute, pressed forward by a force varying from 400 to 800 lb. according to the nature of the rock. Water is supplied through the tube which washes out the débris and cools the diamonds.

Granite and the hardest limestones are penetrated at the rate of 2 to 3 inches per minute, sandstones 4 inches, quartz 1 inch.

The diamond drill is not effective in soft strata such as clay, sand, and alluvial deposits.

Boreholes have been made at the following rates:

In Ironstone formation:

A depth of902feet in54working days
641”48”
434”54”
640”60”