190 The N.Z. Journal of Science and Technology. [May 
retention and for the removal of the carbonate. Thus surfaces of lime¬ 
stone which lie flat or in basin-shaped hollows, whether these are structural 
or not, may contain as a result of concentration in pockets or hollows 
sufficient P 2 0 5 to be called true phosphatic limestones, whereas the normal 
percentage may not warrant the application of the term. Similarly, 
exposed surfaces of limestone may be enriched in phosphatic material from 
external sources, such as the droppings of sea-birds, accumulation of 
bones, &c., of land and marine animals primarily rich in phosphate. This 
enrichment may have taken place during the present period or in some 
distant geological age. The existing stratigraphical conditions of our 
limestones do not lend themselves to concentration or impregnation. They 
are rarely exposed over wide areas with horizontal bedding or gentle 
synclinal structure, the exposures being in general in the form of long 
strips with pronounced escarpments, the greater part of the area being 
covered up with younger detrital deposits and so not exposed to denudation. 
Where they are exposed they are generally tilted, so that all the products of 
decay are rapidly removed. 
The only horizon at which concentration has taken place is the junction 
of the Weka Pass and Amuri limestones and its equivalent stratigraphical 
horizon. This occurred when the upper layer of the Amuri limestone 
formed a sea-bottom during a period of halt in deposition in mid-Tertiary 
times. The remains of marine organisms also contributed to the phos¬ 
phatic content of the layer, so that its upper surface suffered differential 
solution and secondary enrichment at the same time. But these causes 
combined have not succeeded in forming a phosphatic layer which is 
capable of commercial exploitation. 
Phosphatic layers such as those of Florida, Belgium, and northern 
France owe their value to the fact that phosphatic nodular layers, non- 
payable in themselves, have been concentrated by the sorting action of 
water, either of the sea or of rivers, till they have become commercially 
valuable. There does not appear to be any locality in Canterbury where 
this has taken place, and it is unlikely that any such exists. 
The areas which promise best for concentration into payable deposits 
appear to be those from which limestones have been stripped, and not those 
where a limestone covering now exists ; but, as these areas are generally 
covered with a close covering of grass or form a rich agricidtural soil, they 
present no well-marked outcrops, and the locating of such deposits, if they 
exist, must be largely a matter of chance, but it is a chance which must 
be fully recognized. Where the limestones have been stripped from the 
slopes of hills, the loose underlying material, with any phosphatic matter 
it may have contained, has been swept to lower levels and widely distri¬ 
buted over alluvial flats, adding its quota of nourishment to already rich 
soils. It is possible, however, that circumstances may have occurred, 
such as those at Clarendon, Otago, which promoted the concentration 
in situ of a poor limestone into residual matter of high phosphatic content; 
but the conditions obtaining in Canterbury, as far as our experience goes, 
do not encourage the hope that such deposits will be located within its 
limits. 
Possibilities of ultilizing in Agriculture the Limestones and 
Associated Rocks. 
The use of limestone and burnt lime as soil-improvers has been 
practised for centuries, and a consideration of Canterbury rocks in this 
