Geitsi Guhih, an Old Volcano. 
257 
and though the bore-hole records were for several reasons unsatisfactory, 
the facts quoted in the description make the volcanic hypothesis difficult 
to accept. Instances of large blocks in explosion-pipes, such as the piece 
of Waterberg beds 400 yards by 100 yards or less in area which has been 
followed to a depth of 260 feet in the Premier Mine/'' show that the mere 
presence of what might be taken to be the floor of a pipe in a bore-hole 
does not prove that the rock encountered passes across it. No 
cementation by silica or other substances is recorded, though melting of 
comminuted sandstone took place locally. It is noticeable in the papers 
quoted below that the difficulties of the volcanic hypothesis seem to have 
had great effect in gaining the acceptance for the other in the authors'" 
minds, especially the excessive comminution of the quartz grains of the 
broken sandstone and the absence of volcanic rocks. The lack of 
recognizable volcanic rocks is not decisive, nor would the minute splinter- 
ing of the quartz seem to be, and the coincidence in place of a heavy 
meteorite fall and an explosion-crater is not impossible. At present, 
however, Coon Butte cannot be quoted as a case of an explosion-crater. 
Though explosion-oraters, or necks which led to them, from which no 
lava flowed, are known in many parts of the world, the materials filling 
them are usually fragmental volcanic rocks alone or mixed with debris 
from non- volcanic rocks. In certain regions necks have been described 
filled entirely with material derived from non-volcanic rocks so far as they 
are exposed, though in many such cases there must be some doubt on thi& 
point because no mention is made of the results of a microscopic examina- 
tion of the rocks, and it sometimes happens that a rock which is apparently 
without fragments of lava is found to contain such fragments when 
examined in thin section,! In the Stormberg and Drakensberg region 
the volcanic vents of late Karroo age include many without apparent 
lava fragments, though there are probably more which are filled with tuffs 
of a normal type or at least contain some ordinary volcanic rock.| 
In the carboniferous volcanic area of Scotland many of the smaller necks 
and some of the larger ones are filled with non- volcanic material. § 
Agglomerates of non-volcanic rocks are also found in Tertiary necks in 
* Wagner, P. A., " The Diamond Fields of South Africa," 1914, Fig. 9 and p. 21, 
where several other instances are given from blue-ground pipes. An example from a 
large neck on Arran, where a mass of Triassic sediments " several acres in extent " is- 
lying amongst volcanic material, is described by Messrs. Peach and Gunn, in Quart* 
Journ. Geol. Soc, London, Ivii., p. 227. 
t Cf. A. W. Rogers, Trans. Phil. Soc. S.A., vol. xvi., p. 193, and Ann. Rep. Geol. 
Com. for 1905, p. 36 ; tulfs thought to be of non- volcanic material proved, on microscopic 
examination, to have small lapilli in them. 
+ E. H. L. Schwarz, Ann. Rep. Geol. Com. for 1902, p. 54; A. L. du Toit, Ann. Rep. 
Geol. Com. for 1904, pp. 155, 165 ; do. for 1905, p. 130 ; do. for 1911, p. 125. 
§ Sir A. Geikie, Trans. Roy. Edin., vol. xxix., p. 458: "Ancient Volcanoes of Great, 
Britain," vol. i., pp. 57, 426-7 ; and " Geology of Eastern Fife," 1902, p. 204. 
