12 Proceedings of the Royal Society of Victoria. 



sandstone. The microscopic structure of the unweathered 

 rock at the base of the quarry has been previously given. 

 Although this is undoubtedly a tolerably well preserved rock, I 

 do not consider it typical of the trachytoid masses which cover so 

 large an area to the north and west of Coleraine. The majority 

 of my slides have been prepared from the rocks at Cai-apook, 

 which is midway between Coleraine and Casterton. A quarry 

 was opened here about 14 years ago to get stone for building a 

 bridge over the creek, and the glistening crystals shewing on the 

 clean cut surfaces of the blocks as they lay in a pile ready for 

 use arrested my attention. This rock I traced to the quarry 

 mentioned, which is situated on a rise about li miles north of 

 Carapook, and in a line with the Den Hills outcrop a few miles 

 to the east. In hand specimens it is dark green, fissile, almost 

 smooth to the touch, and speckled by the light colored sanidine 

 pervading it. Macroscopic crystals of sanidine are not only 

 abundant in the rock, but they are usually so perfect that when 

 extracted whole, which can frequently be done, the two cleavages 

 parallel to P and M become plainly visible. Owing to the 

 number and size of the macroscopic crystals in the rock, I 

 was able to separate a sufficient weight of them from the matrix 

 for a complete chemical analysis, which gave the following 

 result :- — 



Sanidine Crystals, Carapook. 



Total - 100-60 „ 



With this may be compared the following analysis of the rock 



