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Station at Daspoort, was recently examined in our laboratories, and gave the following results :Moisture
28.16 Alumina, soda, etc.
*Containing carbon dioxide
1.97 per cent.
61.48 This substance, compared with the price of manures at the coast, would be worth about £7 9/- per ton.
B. Other phosphatic manures. Unfortunately, deposits of true mineral phosphates are rare in the Colony, and though several specimens of minerals suspected to consist largely of phosphate of lime have been received from various correspondents, none have proved to be of any value.
However, in many limestone districts, caves—really old underground water courses—exist and in many of these deposits containing the excreta of wild animals, wolves, jackals, and others, bones of these animals and their prey, and in some instances, immense quantities of the excrement of bats, mingled with fine silt, occur. These cave deposits always contain some, and often much, phosphoric acid, in addition to nitrogen, potash, and lime. Such deposits are certainly useful as manures.
Large numbers of samples of this material have been examined in the laboratories, and the results show, as might be expected, great variability.
I append a table giving the proportion of the chief manurial constituents in seven samples, which may be taken as typical of such cave deposits :
3. 4. 5.
6. 7. Phosphoric acid
1.71 26.55 1.58 2.26 Potash 1.29 0.78
0.05 1.14 0.19 Nitrogen 9.7 1.50 0.19 0.32 1.56 2.52
33.14 14.54 7.28 I was a fresh bulky deposit, consisting entirely of bats' dung
from Chune's Poort range in the Zoutpansberg. 2 was from caves near Potchefstroom (bats' guano and silt). 3 was from the large cavern at Wonderfontein (bats' guano and
4 said to consist mainly of wolves' dung (Wonderfontein).
In certain districts it is the custom to employ dried sheep's dung as fuel on the farms. Sheep's kraal manure, used as fuel under the name of “Mest,' was found by Lewis in 1899 to contain (average of 11 samples) :
While E. H. Croghan, in a paper read last year before the British Association at Johannesburg, found 25 samples from Cape Colony and the Orange River Colony contained :
0.55 to 1.68, mean 1.22 per cent. Potash
1.23 to 5.86 3.85 Phosphoric acid 0.38 to 1.28
0.78 the ash left when mest is burnt is free from nitrogen, but much richer in potash and phosphoric acid.
Lewis found, as a mean of 3 samples :-
7.60 per cent.
While Croghan, in 25 samples, found quantities ranging from :
3.74 to 18.57 per cent
In certain parts of the Transvaal are old cattle kraals, used by the natives before the incursions of white men. The deposits overlying these kraals are almost devoid of nitrogen, but still retain considerable quantities of potash and phosphoric acid. A specimen of such deposit, from near Rustenburg, from a kraal said to have been used about a hundred years ago, was found to contain :
This deposit has been largely used by the local farmers with successful results during the last 7 or 8 years, when kraal manure has been scarce.
Another remarkable source of phosphoric acid has come under my notice—the ash of certain Transvaal coals. In a specimen of coal ash from one of the Witbank Collieries I found 5.5 per cent. of phosphorus pentoxide.
Though doubtless the phosphoric acid would be largely present as phosphate of iron, and therefore not readily available, it might form a cheap and useful manure.
The night soil of some of the compounds on the Rand is treated so as to render it odourless by heat. The so-called “ash " left was found to contain :
If the product can be produced in large quantities, and equal to the sample, it should find a ready sale as a fertiliser.
From the above account it will be seen that the natural sources of phosphates in this Colony are limited, and in many instances it may be necessary to purchase imported materials. Superphosphates are well suited for such of our soils as contain, say, one per cent. or more of lime as carbonate, but with the great majority of our soils, poor as they are in lime, basic slag or “ Thomas phosphate ” will probably be the best form of phosphatic manure.
Fortunately, of this important substance, the Colony has large natural resources. Quantities of limestones, some of great purity, exist in many districts, and though I believe that it is true that a large proportion of the lime commerciably obtainable is of poor quality, being badly burnt and containing much insoluble matter and magnesia, this could be easily remedied by proper management, and the choice of suitable limestone.
We have examined many specimens of limestones, and among them were some of excellent quality, capable, if properly burnt, of yielding lime admirably suited for agricultural purposes.
As typical examples of such pure limestones, though it is, perhaps, more correct to describe some of them as calcite, but of which large deposits are said to be available, I may quote the following analyses :
0.2 0.9 43.0 43.3 43.2 0.2 0.2 0.2
4 7.89 0.67 49.93 0.52
As examples of the commercial lime obtainable, the following may be cited :
" Blue lime." Total lime
17.87 Loss on ignition
" Blue lime.”
52.44 17.25 18.35
Good white lime.
92.94 traces 5.50
In some districts limestones do not occur, and I have had correspondence with farmers who were anxious to procure lime for agricultural purposes locally, so as to avoid the cost of transport from a distance. Several substances suspected to be rich in lime have been sent to me, but on examination these minerals have been found to be almost free from that constituent.
The ashes of certain trees have been found to be very rich in lime, and might be used for agricultural purposes when available. Thus a tree from Mozambique was found to yield about 6 per cent. of ash, of which about two-thirds consisted of lime. Another sample, the ash of a tree known as “Mopani, growing in the Tati Concessions country, was found to contain over 55 per cent. of lime, a considerable portion of which existed as carbonate.
As already stated, it is on comparatively few of our soils that potash manures are required.
Probably wood ashes are the most readily available natural source of potash, especially the ash of twigs, brushwood, etc.
Should imported manures be used, preference should be given to sulphate of potash. On no account is it advisable to use the lowerpriced Kainite, which is open to the objections of involving a much greater cost in transport for the same quantity of potash, and to being contaminated with large quantities of saline matter, which is not only useless, but may prove very harmful.
In conclusion, I would emphasise the importance of utilising as fully as possible the natural manurial resources of the country, and thus avoiding the expense which is involved in the purchase of imported manures. Indeed, so high are the prices of the latter, when the cost of transport is included, that it is often a matter of difficulty to know whether one is justified in recommending their use, and whether the undoubted increase in yield which would follow their application would pay for their cost.
Greater attention should be paid by the farmers to the preservation and restoration to the land, of all the waste products of the farm, the use of green manuring, and all means by which the muchneeded combined nitrogen, phosphates, and lime may be conveyed to the soil.
OTHER EARTH MOVEMENTS.
BY JOHN MILNE, F.R.S.
At the present time the greatest seismic activity in the African Continent is to be found in the high lands of Algeria and in the vicinity of the Great Lakes, and Abyssinia. If from the former of these districts we travel Eastwards in the direction of Tunis, or Westwards through Morocco and turn Southwards down the Western side of the Continent, the activity rapidly decreases. A similar decrement is met with if from the central region we go Northwards down the Nile Valley or Southwards towards Cape Colony. Not only is the frequency small, but the shocks themselves
are insignificant. They are local in character, and probably represent slight adjustments on lines of existing faults. For ten years at least Africa has not produced a single world-shaking earthquakę, the inference from which is that during this period no large fault has been created. If, however, we regard the African Continent as a mass which extends Eastwards to the floor of the Indian Ocean, we find that the sites of several megaseismic efforts have been traced to this submerged frontier. From the changes which have taken place in soundings after a large earthquake which has originated beneath a sea or ocean, but more particularly from measurements made on land, when it has been found that valleys have been contracted, and the lengths of trigonometrical lines have been altered and from other observations, the conclusion arrived at is that a world-shaking earthquake originates from the faulting, shattering, and the displacement of an area only to be measured by many thousands of square miles. If we had a knowledge of the depth to which the faulting extends, a cubic measurement might be made of the magnitude of these molar displacements. Inasmuch as they transmit sufficient energy through the crust of our earth to create movements which may be recorded at the antipodes of their origin, it seems probable that the displacement downwards extends to a considerable depth. If we regard the crust of our world as a layer of materials which conveys elastic vibrations at about the same rate as they are conveyed by the rocks we see, then seismological investigations indicate that this covering is less than 30 miles in thickness. In relation to the area which is displaced, fracturing to this depth, or, at least, to a large fraction of the same, might be compared to the formation of the tiny cracks we sometimes see in the varnish covering an ordinary globe. The origins of the displacements, along the line of the Mozambique synclinal have apparently been too far from the African coast for the resultant vibrations to be felt, but they have been recorded in very distant countries. At the present time in Africa the British Association type of seismograph, which is not adapted to record local earthquakes which can be felt, but only to record unfelt teleseismic motion, is only to be found at Cape Town and Cairo. Forty other similar instruments are installed in Europe, Asia, America, and Australia. Capt. H. E. Lyons, R.E., of the Egyptian Survey Department, now proposes to establish observing stations at Khartoum and Lake Victoria. The