BY H. I. JENSEN. 113 



(b) Sedimentary Rocks. 



Sp. No.91. Quartzite. Loc: Noosa Heads 



This rock is of a dark colour, and from handspecimens it is 

 impossible to say whether it is quartzite or microgranite. It 

 overlies the quartz-diorite at Noosa Heads. 



Under the microscope it is seen to be allotriomorphic granular, 

 fine-grained, and consisting of irregular crystals of quartz and 

 felspar cemented by a micaceous base. The abundance of felspar 

 and the irregular, subangular shape of the grains serve to show 

 that the sand si one from which the rock is derived was probably 

 tuffaceous. The cement was originally clayey. The quartz 

 diorite intrusion has effected the metamorphism. 



Name: Tuffaceous Quanzite. 



The sandstone and quartzites overlying the hypabyssal 

 Pt. Arkwright rocks vary in coarseness from that of grit to fine 

 conglomerate. They are, therefore, ' gritty quartzites,' 'quartzite 

 conglomerates,' and sandstone conglomerates. 



The sandstones and interbedded shales of Trias-Jura age in the 

 East Moieton and Wide Bay Districts, there is no need to 

 describe in detail. They are almost all of the types usually met 

 with, as in the Hawkesbury Series (if New South Wales. Some, 

 however, are very rich in iron and contain ironstone concretions. 

 Some are very tuffaceous. This is especially the case in the 

 Woombye and Maroochy districts; and it is such a sandstone that 

 the Noosa mass has altered to quartzite. The sandstones around 

 Buderim Mountain contain a number of obscure remains of fossils, 

 which are very suggestive of Echinoderm and Maccoyella casts. 



The shales found interbedded with the Trias-Jura sandstones 

 are of two main varieties. — (a) Black carbonaceous shales, often 

 containing good fossil remains, such as stems and leaves of 

 Thinnfeldia ortontopteroides and its var. falcata : at Petrie's Ok., 

 Nambour, these fossils are very abundant in an out-cropping 

 seam of coal and carbonaceous shale, (b) Yellow, very soft and 

 fissile clay shales. In these I have never been able to detect 

 fossils. They occur in strata of various thicknesses, varying 

 from a few inches to twenty feet or more. 



