IS THERE GOOD COAL IN SOUTH CANTERBURY?

Temuka Leader, Volume I, Issue 89, 23 October 1878, Page 2

IS THERE GOOD COAL IN SOUTH CANTERBURY?

(to the editor of the temuea. leader.) Sir, —Will you kindly grant me space in your columns to air a few of the thoughts that I entertain on the above subject I The question with which I head my letter is not a question of present’ public interest, and I am rather doubtful of exciting a public interest in it. Some years ago the limestone downs of the Kakahn were hopefully thought to hide a useful deposit of coal, several outcops of seams having been found with but little trouble. These seams, however proved to be thin, and their quality but poor. Whether the prospectors were thereby disheartened, or whether further search proved unfruitful, I do not know, but for the last few years nothing, I understand, has been done in the direction of prosecuting the search for better seams. Ido not place much reliance on my own geological conclusions —and, unfortunately, I have none other to rely upon in considering the case —but I am of opinion that the Kakahn seams belong, if not to the true carboniferous series, at least to a series much older than many of the lignites and brown coals that are profitably worked in other parts of New Zealand. A thin seam crops up in Pleasant Valley, just below the red cliffs, and another appears in the bank of the Waihi river, about a mile and a half above Messrs Webb and Penny’s saw-mills. If these three outcrops are supposed to be portions of one continuous formation, we may also suppose that that formation possessed, some, breadth as well as the considerable y -length indicated by the distance between. ■ the most widely separated outcrops. Whether the coal found at Mount SomersVand further away still, at the Malvern , rtlills), belongs t<> the same age i have no means of knowing, and would therefore prefer not to mention tiiose deposits except to suggest that if they are portions of the same beds with the first mentioned, w.e may safely suppose a greater breadth in our rude estimate of the extent of the ' ■ hole. ■

It is no easy matter to imagine what was the contour of the country when the coal found in the skirts of these mountains was deposited. For my own part, I despair of achieving the task. But at any rate it does not seem probable that where the plains' are now spread out seawards the land of the coal era was much higher than that belt whereon the coal now found was deposited. It is true that it may have been so much lower as to have been under water,-salt or fresh. If it were not so, there is at least a chance that coal was deposited over more or less of the entire area. Supposing this to have been the case, where is that coal now ?

After the coal age, a long period elapsed during which the land was overflowed by the sea. The thick beds of limestone which overlie the coal at the Ivakahu, and the numerous and perhaps collectively thicker beds of shelly sand and stone which cover the coal of the Waihi, testify to this. It is possible that the irruption of ’ the sea through change of the surtace level occurred in such a way as to destroy to a great extent the previously found coal bed. It is possible, but is it probable ? Much depends on the time the change occupied. If it occurred very slowly, the previous surface may have been destroyed by the advancing beach surf, but if it occurred suddenly or rapidly, the previous surface Would be covered with • out being much affected, and soon securely buried beneath a marine deposit, There is, I expect, nothing to show how the change occurred. But assuming that the bed was not destroyed by the irruption of the sea, it follows that it must still be preserved at some greater or less depth beneath the present surface. , Another important point to consider is, are the thin and imperfect seams which crop qpt on the skirts-of the hills to be taken to indicate the average valim of the field 1 ? If we could suppose that these outcrops were the outskirts of the field at the time of its being formed, we might safely conclude that much better coal would be found at a distance from those outcrops. If we could be sure that a range of higher ground occupied the place of the present hills, we might safely make that supposition. But we can scarcely be sure of this. It is certain, at least, that the present hills have received much, if not the whole, of the present elevation since the deposition of the coal. The section of thejeoal bed, and of the marine beds evposecl in the banks of the Waihi, show that both series extended further westward than their present boundaries, i how far, it is impossible to say. ■ * v To sum up roughly what I have already said :—Marine beds crop up along the ■Skirts of the hills, rising with varying angles from beneath the shingle of the plains, and therefore underlying the -v' t'Hjm-’. Coal seams appear beneath the

'marine beds at tlie foot’ of the bills, and possibly extend for a considerable distance eastwards from wiiere they crop ■out. If they do so it is not nnpr< 1 able that they may be found to improve in thickness and quality at some dis lance from their outcrops. Whether there really exist ; a hed of coal beneath our southern plains, and its value if their does, can only he asceitained by sinking or boring through the upper bed of shingle, and the marine beds which underlie it. The question is, are the probabilities of its existence, and ‘of its being profitably worked if found, sufficient to make it worth while to institute a search for it 1 If the search were undertaken, I think that Pleasant Valley offers the most 'favourable site for the ‘operation. I have Already said that coal crops out in this v illey. This coal, however, does not, _in fPiivMny opinion, belong to the same as that which appears under the Kakabu hi-Is, and in the Waihi river. There is no trace of overlying marine beds. It is covered, as far as I could ascertain, only by a deposit of fine and pure quartz shingle, strongly cemented together. Just such a deposi appears, but in smaller quantity, above the marine beds in the Waihi. I conclude, therefore, that the valley seam was formed after the land had again emerged from the sea which had so long rolled ever the Kahahu and Waihi seams. The fact that this newer -coal here appears at the surface, affords a valuable suggestion respecting the o’der bed. The forces which acted to produce the elevation of the Geraldine downs at a ■comparatively late period in bringing up, as they did, the newer seam found in the would also bring, nearer to the surface the older and more deeply buried ■seam. , _ If the depth at which the material is buried is an important fact in procuring a good coal, the supposed South Canterbury field has been well favoured in this respect. The immense thickness of gravels and clays shown in a section in Pleasant Valley, and the perhaps thicker marine beds beneath these, both overlying the coal, must have supplied a suffi cient consolidating pressure I do not expect that the simple arguments I have used in endeavouring to show the probable existence of coal beneath our feet will be considered sufficient, but I do hope that I have urged enough to induce others, better fitted for the task, to expend a little time in a consideration of the available facts, in order to arrive at a more decisive answer than -lean give to "the question, Is it probable that there is a good coal field in South Canterbury ? I am. &c., P. V.