88 ROCKS USED IN THE MANUFACTURE OF TROXATTAS. 



quently the colour is streaky, darker and lighter coloured 

 bands regularly alternating, particularly in the grey 

 varieties. 



Tronattas made of hornstone are unquestionably the 

 most common. As stated in a previous paper, horn- 

 stone was obtained from Clarke's quarry (Mount Com- 

 munication), Johnstone's quarry (Coal Hill, Melton- 

 Mowbray), Hutchison's quarry (Front shelves run, 

 Beaufront, Syndal), Nichols' quarry (Melton-Mowbray), 

 and probably also from Bisdee's quarry (Great Lake) 

 and Walker's cjuarry (River Plenty). x\t most of these 

 quarries a dark blue hornstone was obtained, only at 

 Nichols' quarry and the eastern part of Hutchison's 

 quarry a grey hornstone occurs. This seems to indicate 

 that the blue hornstone is of more frequent occtuTence 

 than the grey one, a fact which is borne out by the 

 number of implements manufactured from either rock. 



The hornstone has a peculiar chemical feature not 

 observed in the other kinds of rocks used for imple- 

 ments ; when exposed to the action of the atmosphere 

 it becomes coated with a peculiar earthy-looking crust 

 of whitish or more frequently yellow or rusty-brown 

 colour. This " patina " so compbtely covers the rock 

 that it IS frequently impossible to ascertain its true 

 colour without breaking the specimen, or at least strik- 

 ing off a small particle. There can be not the slightest 

 doubt that the patina is the result of a superficial 

 chemical decomposition, the more soluble elements 

 were removed, while the less soluble, in particular iron 

 and alumina, were left behind. But not only do the stone 

 implements show this crust, in a still higher degree is it 

 exhibited by the rock as found in the quarries in situ, 

 where it often attains as much as three-quarters of an 

 inch in thickness. 



The tronattas are usually covered with a thin patina 

 only, which in no way obliterates the sharp edges pro- 

 duced by chipping. There are, however, other speci- 

 mens in which the patina has reached such a thickness 

 that the original chipping begins to disappear. There 

 can be no doubt that the thickness of the patina is a func- 

 tion of time, and the thicker it is the older is the imple- 

 ment. Unfortunately no data are available, to estimate 

 the number of years it takes to form a patina of a certain 



