REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1901 P25 



had been reached. In the neighborhood of the amygdules 

 specially it seems quite certain that at least some glassy base 

 remained. Irregular masses of calcite are frequent throughout, 

 and the presence of some olivin is indicated by the crystal out- 

 lines remaining, though the mineral is so utterly decomposed 

 (showing a mixture of quartz, calcite and opaque uncertain 

 material) that no positiveness is possible. 



The other rock is somewhat coarser. It shows rather abund- 

 ant olivin, wholly altered to a greenish, chloritic aggregate. The 

 determination is based on the shape and size, it having been 

 plainly the first mineral to form. The feldspars are in two 

 sizes, both tending to the long, lath shape, and mostly showing 

 twinning. The greatest observed extinction is 22°, but the 

 majority are much less, between 10° and 15°, and most of the 

 laths which show no twinning extinguish nearly parallel. There 

 are likely present therefore both labradorite and andesin, and 

 perhaps oligoclase as well. The mineral is not fresh, being 

 largely altered to calcite and quartz. The interspaces are filled 

 by a mixture of calcite, and chlorite aggregate, likely the result 

 of augite decomposition. Considerable magnetite is present. 

 The rock seems to be an olivin-diabase-porphyrite, and like many 

 olivin diabases shows considerable preponderance of feldspar 

 over augite, resulting in only a rough approximation to the 

 ophitic structure. 



Both rocks are amygdaloidal. The universal filling is calcite, 

 with an outer rim of clear, glassy quartz, commonly very narrow 

 and sometimes absent. The two are invariably separated by a 

 sharp, narrow, dark band of uncertain nature. The quartz 

 was of course deposited first, no doubt from silicious waters 

 while the material yet retained some residual heat. The calcite 

 was later, perhaps much later. 



Both these rocks have the characters of surface lavas, and 

 could not have solidified at any great depth beneath. 



The rock from south of the fault is not amygdaloidal and of 

 considerably coarser grain. It is also the least altered of any, 

 and is a perfectly normal olivin diabase. * Minute, glittering feld- 

 spar laths are easily made out by the eye. 



