388 The N.Z. Journal of Science and Technology. [Dec. 
Detailed Description of the Split. 
On the steep sides of the small gullies west of the little hill mentioned 
above continuous outcrops of coal may be seen for several chains. A shale 
parting appears in these at 2J ft. to 3 ft. below the roof of the seam, and 
as it is traced westward greatly increases in thickness. The shale, more¬ 
over, in part or whole, passes into sandstone, which in its turn passes into 
current-bedded grit. The following sections are typical :—- 
(1.) 2J ft. coal (upper seam), 1 ft. sandstone, 12 ft. coal (floor not seen). 
(2.) Nearly 3 ft. coal, 5 ft. shale and sandstone, 7 ft. coal (floor not seen). 
(3.) 3 ft. coal, 6 in. shale, 6 ft. shaly sandstone, 3 ft. sandstone which 
westward becomes thicker and coarser, 6 ft. coal (floor not seen). 
(4.) 3 ft. coal, 6 ft. shale and shaly sandstone, 40 ft. grit and sandstone, 
outcrop of lower seam obscured. 
A few years ago the Westport-Stockton Goal Company drilled numerous 
bores to the westward of the outcrops just described in search of the lower, 
or Matipo, seam. Some of the results obtained were as follow :— 
Bore No. 7 or 6e : 101 ft. grit, sandstone, &c., 18 ft. coal. 
Bore No. 7e : 104 ft. grit, &c., 10J ft. coal. 
Bore No. 4e : 117 ft. grit, &c., 5 ft. coal. 
Bore No. 1 : 137 ft. grit, &c., 7-J ft. coal. 
Not far from each of the bores mentioned the upper, or Mangatini, seam 
outcrops, so that it is possible to estimate with a fair degree of accuracy 
the total thickness of the beds separating the Mangatini and Matipo seams, 
and to construct the partly ideal section mentioned above. 
Explanation of Split. 
Two general explanations of splits in coal-seams have been advanced, 
both of which seem plausible, and both of which may be correct in special 
cases. Since, however, the splitting of coal-seams is part of the wider 
problem of their origin, the adoption of one explanation or the other is by 
no means a matter of indifference. In his little book The Natural History of 
Coal Newell Arber discusses at considerable length the mode of formation of 
coal-seams. He considers that the “ growth -in-situ,” or autochthonous, 
theory is much more generally applicable than the “ drift,” or allochthonous, 
theory, and accordingly combats the view urged by the drift theorists that 
the splitting of coal-seams is difficult to account for on the growth-in-place 
hypothesis. After mentioning instances of splits he goes on to say,— 
“ The splitting of coal-seams is probably more frequent than is generally 
imagined, for it is only where the main coals of the district are affected 
that the fact becomes of economic importance. No doubt the explanation 
is to be sought for in the oscillations of the earth’s surface in Carboniferous 
times, when, as we have seen, there were alternate periods of elevation and 
depression. In South Staffordshire and Warwickshire, instead of an even 
depression, the ground appears to have undergone a local tilt, the southern 
area being somewhat raised and the northern depressed. Thus wedge-like 
encroachments of marine sediments overwhelmed the accumulating vegetal 
material unevenly to the north, while the raised southern portion of the 
seam escaped. A series of such depressions and elevations following one 
another, of a like nature and constant axis, would appear to explain the 
facts presented by the splitting of coal-seams, and if this is the case the 
matter has no particular bearing on the truth of either theory.* 
* E. A. Newell Arber, The Natural History of Coal . pp. 112-13, 1911. The theory 
that splits in coal-seams are caused by differential movements is an old one. It was, 
for instance, advocated by Adolph Eirket in 1894, and probably also by F. C. Grand ’Eury 
at a still earlier date. 
