BY FRITZ NOETLING, M.A., PH.D., ETC. 8g 



thickness. The process must, however, be a very slow 

 one. At Maryvale I found some specimens which were 

 unquestionably re-chipped. Though this must have been 

 done at the very least 75 years ago, the later fractures 

 did not show even a trace of patina, but exhibited the 

 deep jet-black of the hornstone, strangely contrasting 

 with the whitish patina which covered the whole sur- 

 face. This being so, I doubt whether we will ever be 

 able to ascertain this factor, because it is imquestion- 

 able that centuries must lapse before any patina of any 

 appreciable thickness is formed. There is, however, no 

 doubt that if by the combined work of generations this 

 factor could be ascertained, one of the most valuable 

 data for the estimation of the length of the past would 

 be obtained. 



When exposed to the action of blown sand, the 

 hornstone takes a fine polish, exhibiting a peculiar shiny 

 lustre, quite different from the original dull one. Blown 

 sand, however, apparently prevents the formation of a 

 patina. 



The heat of fire affects the hornstone in a peculiar 

 way; the surface becomes covered with a number of fine 

 cracks, generally running in parallel lines, and connected 

 by short cross cracks. It appears that these cracks are 

 only superficial, and never penetrate deeply into the 

 stone. If such a cracked hornstone is exposed to the 

 air parts of its surface commence to break off, leaving 

 a rough jagged surface, which greatly differs in appear- 

 ance from the even, smooth surface produced by flaking. 

 There is no doubt that in this v/ay the finest tronatta 

 can be destroyed beyond recognition. 



The natural crust which is still preserved in a 

 number of specimens is always more intensely affected 

 by the heat than the original stone. It breaks into a 

 number of irregular polygonal pieces, strangely re- 

 sembling a tesselated pavement in miniature. 



Hornstone flakes exceedingly well, and with a little 

 practice large flakes, showing- a fine, flat face and a sharp 

 cutting edge can be struck off a larger block. There 

 can be no doubt, however, that in certain instances the 

 blow must have been carried out with tremendous force. 

 The largest specimen I have so far found measures 7.4 



