122 ZWARTKOPS BORE AND THERMAL SPRING. 



inside that 1,330 feet of 9-inch casing, and so on with 8-inch, 

 6-inch and 5-inch, which is the innermost size, and was designed 

 to be carried down to 4,000 feet. The total length of casing in 

 this bore is a little over two miles, and represents a money value 

 of about £1,400. If the bore had to be abandoned the greater 

 part of the casing could be recovered, but in this case it has to 

 be left in to preserve the bore from closing. 



The derrick, together with the engine and gearing, had to 

 be covered in as a protection against the weather and for night 

 work. The boiler is placed at a regulation distance from the 

 bore in case of an outburst of gas, which usually accompanies 

 oil. 



The serious work of drilling began after passing through 

 the layer of boulders and running sand in April, 1908, and drilling 

 was stopped on the last day of October, 1909, at a depth of 3,620 

 feet. After entering the bed of blue clay at 80 feet, bands of 

 marl, sandstones, etc., were passed through down to 917 feet, 

 where a bed of sandstone 70 feet thick was met with ; then more 

 clays, shales, and sandstones in bands to 1,570 feet, where a 

 second bed of sandstone was met with no feet thick, and again 

 more marl and shales, with bands of sandstone to 3,234 feet, 

 where the beginning of the sandstone was reached that at 3,404 

 feet yielded the first of the hot spring; this sandstone remained 

 till the bottom of the bore at 3,620 feet. 



The rate of progress at first averaged about 14 feet per day, 

 but for the latter half down to 3,200 feet only 8 feet; this 

 included time occupied in changing bits and putting in casing. 

 From 3,200 feet to 3,400 the progress was even slower owing to 

 the increased depth, but after the spring was struck at 3,400 feet 

 the upward pressure of the water was so great that the tools, 

 although weighing about seven tons, could make very little pro- 

 gress, a full blow could not be struck, the drill seemed to rebound 

 as from a cushion, and about \ l / 2 feet per day was the 

 whole progress, and the result was a little coarse, gritty sand, 

 much stained with iron, which was shot up by the water. The 

 pressure gauge placed on the pipes after the bore was capped 

 registered upwards of 100 lbs. to the square inch. 



Three springs of fresh water were passed through at 960^ 

 1,250 and 1,530 feet respectively, also a salt brine spring at 2,480 

 feet. All of these rose to the surface, but were shut off by the 

 casing in turn as the various lengths were put down. All these 

 springs were cold and gave no indication of the hot spring met 

 with 900 feet below. 



From 1,430 feet to 2,670 feet a variety of small shells was 

 found embedded in the clays and in a fairly good state of pre- 

 servation, although the tools destroyed a large number. Through 

 the good offices of Dr. A. W. Rogers, of the Government Geo- 

 logical Department, these were sent to Dr. Kitchen, of the Geo- 

 logical Survey of Great Britain, who reported and classified them, 

 assigning to each of the eight samples sent the probable geological 



