BY H. I. JENSEN. 121 



disintegration and rearrangement of the original constituents 

 mechanically to form a new rock. The Cooran granite consists 

 essentially of quartz, orthoclase largely altered to kaolin, and 

 muscovite. It is a very acid type of muscovite granite. 



The granites of the Woondum Tableland (N.E. of Cooran) are 

 similar but much fresher. They are traversed by numerous veins 

 and dykes of aplite, quartzite and reef-quartz formed in the 

 pneumatolytic period. 



General remarks. — It should be remarked, in leaving the 

 Plutonic Rocks, that the earliest igneous intrusions of the 

 district, the gabbroic rocks, were calcic; the next, the quartz 

 diorites, tonalites and granites, of which the Neurum, Terror's 

 Ck. and Woodford granites are examples, are also calcic, but as 

 shown by the nature of the felspars, contain a considerable sodic 

 element, and so form a transition group to the highly alkaline 

 Post-Triassic intrusives. The gabbros were probably Pre-Carbo- 

 niferous injections; while the granites are of Carboniferous or 

 Permo-Carboniferous age. 



(d) Hypabyssal Rocks. 



Sp.No.36. Granophyre. Loc: near Wardrop's Selection, the 

 Toolburra Range, near Yandina. (Plate xii.,. figs 7-8). 



i. Handspecimen of reddish colour, somewhat weathered. 

 Close inspection reveals quartz, orthoclase and hornblende. 



ii. Microscopic examination. — (1) Texture (a) crystallinity, 

 noncrystalline; (b) grain-size, variable between fine and medium; 

 (c) fabric — allotriomorphic, graphic and micrographic. 



(2) Constituents. — Essential, orthoclase and quartz; Minor, 

 chlorite, hornblende, magnetite and hematite. 



(3) Remarks on minerals. — The pinkish orthoclase gives its 

 colour to the rock. It is weathering to kaolin. The hornblende 

 is corroded and is decomposing to chlorite. It is present in only 

 diminutive proportions. The magnetite is undergoing decomposi- 

 tion to hematite. 



