390 The N.Z. Journal of Science and Technology. [Dec. 
influx of sediment taking the place of vegetal matter which normally would 
have accumulated on the spot so as ultimately to form a thick coal-seam. 
It is also evident that the “ growth-m-sf^ ” or autochthonous theory, 
though applicable, does not explain the formation of the Mangatini-Matipo 
coal-seam as satisfactorily as the “ drift ” theory. Moreover, the explana¬ 
tion of splits and of stone lenses in coal-seams based on the shrinkage of 
vegetal matter during its conversion into coal appears to be much more 
likely to fit the majority of cases than the earth-movement theory supported 
by Arber. Again, as a rule, there is no need to suppose that the coal 
substance has been partly removed by erosion before the deposition of the 
stone lens or wedge. Many so-called “ washouts ” may also be reasonably 
explained without recourse to an erosion hypothesis.* 
In conclusion, one may repeat the statement that the occurrence of 
splits in coal-seams is more consistent with the allochthonous, or “drift,” 
theory of coal-formation than the opposing “ growth -in-smi ” theory, 
especially those forms of it which assume the existence of terrestrial 
conditions similar to those of a peat bog. So far as New Zealand is 
concerned the drift theory is clearly applicable to the majority of the coal- 
seams, none of which extend over areas comparable with those of the world’s 
more important coalfields. This statement is not intended to exclude 
vegetation grown in situ from our coal-seams, but to emphasize the probable 
predominance of transported material. While it may be true that in the 
majority of foreign coalfields the reverse is the case, most modern writers 
seem to agree that in many cases the transportation of vegetal matter is not 
a negligible factor in the formation of coal.f From an academical point of 
view it is all very well to say that the drift and in-situ theories are 
“ reconciled in the more advanced minds, but in practice it is necessary 
to determine as exactly as possible how a given coal-seam has been formed, 
a task which in the present state of our knowledge is difficult, and likely 
more often than not to lead to sharp divergences of opinion. Hence in the 
study of a coalfield the accumulation of data relevant to the mode of 
formation of the coal in that particular area is all-important. The chief 
use of existing theories is to help the geologist and the miner to note 
essential facts which might otherwise be overlooked. 
The Application of a Change - of - volume Factor to the 
Correlation of Coal-seams and Coal-bearing Strata. 
By P. Gr. Morgan, New Zealand Geological Survey. 
It is a matter of common knowledge that the various coal-seams in a coal- 
measure series are not, as a rule, strictly parallel to one another. In this 
paper it is suggested that one of the main causes of variation in the thickness 
* On 8th January, 1919, Professor P. F. Kendall read a paper before the Geological 
Society of London, entitled “ On Washouts in Coal-seams and the Effects of Contemporary 
Earthquakes.” So far as can be gathered from a report of this paper in the Colliery 
Guardian of 24th January, 1919, Professor Kendall’s views differ considerably from 
those advanced above. 
[Note.- —Since this paper and the one that follows were forwarded to the Editor of 
this Journal I have seen a review of another paper by Professor Kendall, “ On the 
Splitting of Coal-seams by Partings of Dirt. Part I : Splits that Rejoin,” published in 
Trans. Inst. Min. Eng., vol. 54, p. 460, 1918 (title, &c., quoted from the Geological 
Magazine, dec. vi, vol. v, No. 10, Oct. 1918, p. 477).—P. G. M. 3/12/19.] 
-j- This statement is illustrated by the somewhat complicated classification of the 
leading modes of accumulation of coal-forming vegetable matter given by Marie C. 
Stopes and R. V. Wheeler in their Monograph on the Constitution of Coal, p. 2, 1918. 
+ M. C. Stopes and R. V. Wheeler, loc. cit., p. 1. 
