Manurial Needs and Resources. 153 



■^Containing carbon dioxide 1.97 per cent. 



nitrogen 1.27 ,, ,, 



t Corresponding to phosphate of 



lime 61.48 ,, ,, 



This substance, compared with the price of manures at the coast, 

 would be worth about £,"] 9/- per ton. . 



B. Other phosfhatic 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 under- 

 ground 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 cf 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 : — 



1 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 

 silt). 



