Tidal Phenomena at Inland Boreholes near Cradock. 71 
in tank A. Accordingly further attempts to measure these variations 
were deferred until such time as the recording apparatus could be 
constructed. 
Meanwhile I directed my attention to the question why No. V. should 
be exhibiting marked variation of yield while Nos. II., III., and IV. were 
nearly constant, showing little if any variation, although all four were 
giving forth high-temperature water with strong sulphurous odour and 
inflammable gas. 
I closed both No. V. and No. IV. No. V. was closed by means of a 
wooden plug, through which a round hole was bored and a few feet of 
glass tube inserted to fit tight and stand in a vertical position. The water 
at once mounted in the glass tube to about 5 inches above the datum line, 
and then in the course of an hour slowly rose 7 inches higher. 
Thus the potential level of No. V. is less than a foot above the level at 
which the water usually stands in tank A. 
About an hour after the two boreholes had been closed No. IV. was 
opened again. Meanwhile I closely observed the water-level in the glass 
tube at No. V. The. instant of opening No. IV. was signalled to me by 
Mr. Eayner by means of a gunshot. Exactly 60 seconds after I heard the 
shot I noticed the water-level in the tube shiver and drop about inch. 
Then it steadily dropped about f inch per minute for a few miautes, after 
which the rate of fall diminished slightly. Twenty minutes after the first 
shiver the level had fallen about 4^ inches in the tube. 
It was clear then that No. IV. and No. V. had a close connection. 
I failed, however, to obtain any evidence of a similar relationship 
between No. V. and the distant boreholes Nos. III. and II. I afterwards 
found that No. III. reacted to the opening or closing of No. II. 
With a levelling instrument and surveyor's staff I next determined the 
relative heights of the boreholes to be as follows : — 
Datum mark in water at No. V. is 3-53 feet above level of No. IV. orifice 
,, ,, 6-70 feet above orifice of No. II. ,, 
„ 16-72 feet above orifice of No. III. ,, 
More recently I have been able to relate these levels with sea-level as 
follows. The Government Irrigation Department has made a survey 
traverse in connection with a proposed irrigation furrow which was to be 
made through the farm. This traverse connects with the railway survey 
levels at Mortimer, which latter survey of course goes down to the coast 
at Port Elizabeth. 
Peg 91 of the Irrigation Survey is situated within 100 yards of No. III., 
and on levelUng from this peg I found that No. III. Hes 8'95 feet lower. 
