192 The N.Z. Journal of Science and Technology. [May 
effect, but that the frequent use of such a limestone, containing even a small 
percentage of phosphate, would tend towards the maintenance of fertility 
cannot be denied. It is arguable, therefore, that the low cost of a readily 
accessible supply may outweigh the disadvantage of its impurity, considering 
that some of the impurity has a value. 
Another way in which these cheap though rather impure supplies of 
limestone may find application is as a “ filler ” for the purpose of diluting 
the concentrated fertilizers used in the preparation of the mixed manures 
so popular among farmers. The use of gypsum has long been practised, 
but supplies of this material are now scarce and dear, if not altogether 
unobtainable. Ground limestone has already been used considerably as a 
substitute, and in the main with satisfactory results. The chief objections- 
to it are the facts that it “ reverts ” soluble phosphate, and that the 
mixtures containing it are apt to set, necessitating recrushing. 
From among a number of localities that could be cited the best from 
the point of view of access by rail are Waikari, in North Canterbury, and 
Waihao Forks and Cave, in South Canterbury. At Waikari there is an 
outcrop of Amuri limestone just behind the church and within a few 
hundred yards of the railway. This is a stone of considerable purity— 
much purer than the deposit of slip material that has already been worked 
just behind the Great Northern Hotel. At Cave there is an old quarry 
beside the railway, and though the stone is not of the highest purity it 
could be worked very cheaply. At Waihao Downs there is an escarpment 
running parallel to the railway and very easy to work. The stone in its 
natural state contains 50 to 70 per cent, of CaC0 3 , as well as 2 or 3 per 
cent, of tricalcic phosphate and some potash. It should be very useful as 
a “ filler.” A stone of much the same quality but richer in phosphate 
occurs in a gully about a mile from Waihao Forks Railway-station. The 
Mount Somers limestone has already been mentioned. 
Greensand is another material that seems admirably adapted for use 
as a “ filler.” In addition to containing a varying small percentage of 
phosphate, it also contains potash, often in considerable amount, as well 
as carbonate of lime. Morgan* cites samples from the Gisborne district 
yielding 1-98 per cent, of K 2 0 and over 28 per cent, of CaC0 3 . A deposit 
at Burnside, near Dunedin, contains 3-35 per cent, of P 2 0 5 4*12 
per cent, of K 2 0. The effects of burning such samples are well worth 
investigating ; the percentages of P 2 G 5 and of K 2 0 would, of course, 
be relatively increased, and where much CaC0 3 is present it is probable 
that some of the potash would be rendered soluble. Such material, 
though certainly not rich enough for direct application as a fertilizer, 
would be very valuable for soil-improvement if used in quantity. But 
it should be specially suitable for use as a “ filler,” since it would not 
only add phosphate, but would possibly prove in itself a sufficient source 
of potash in mixed manure, our soil requirements in this respect being 
quite limited. 
A greensand collected by us at Waikari contained 3-05 per cent, of K 2 0 
and 0*33 per cent, of P 2 0 5 ; the percentage of CaC0 3 was low ; the loss 
of weight on ignition was 6-86 per cent. 
In concluding this report we wish to express our indebtedness for 
valuable assistance received from various landowners, and especially from 
Mr. Charles Kerr, of Cave, and Mr. George Pitcaithley, late of Waimate. 
* P. G. Morgan, Potash in New Zealand and other Countries, N.Z. Journ. of Agr., 
vol. 14, p. 257, 1917. 
