146 ENOGGERA GRANITE AND ALLIED INTRUSIVES. 



The oldest unaltered sediments occurring in the vicinity 

 of these igneous rocks, are the series known as the Ipswich 

 beds. These, although they are not actually shown on 

 the geological map accompanying this paper, occur almost 

 immediately outside it, good sections being shown on the 

 Brisbane River near the mouth of Oxley Creek and at 

 Corinda. They are made of sandstones, conglomerates, 

 and grits, interspersed with layers of shale, while almost 

 at the base of the series is the extensive deposit of volcanic 

 ash, known as the Brisbane Tuff. The basal beds of the 

 system are to be seen in a number of sections in and around 

 Brisbane resting unconformably on the Brisbane schists. 

 They contain a rich fossil flora of mesozoic forms, a 

 consideration of which indicates a Trias-Jura age for the 

 formation. 



Above the mesozoic sediments are a series of con- 

 glomerates, grits and clays. These beds, in which a number 

 of fossils of dicotyledonous plants have been found, are well 

 displayed around Sherwood, and are generally assigned to 

 the Tertiary period. 



The most recent deposits are river alluvials which 

 a-re to be seen at a number of points along the banks of 

 the Brisbane River and Kedron Brook, and to a less 

 extent those of Enoggera and Cubberla Creeks. 



The metamorphic rocks are represented by a very 

 extensive series of altered sediments known as the Brisbane 

 schists. These schists are extremely important in the 

 present connection, in that it is with them that the igneous 

 masses here dealt with are almost invariably associated. 

 They are undoubtedly the oldest rocks in this portion of 

 Queensland, and occupy the major part of the area under 

 discussion. The series is made up of mica schists, slates, 

 and shales, which have undergone a varying amount of 

 secondary alteration by silicification. They are markedly 

 schistose, and generally exhibit very noticeable contortion. 

 Jensen, in speaking of these Brisbane schists, remarks 

 that they '" are so crushed, folded, foliated and faulted 

 that they must be assigned to the middle zone "^ in 



1. H. I. Jensen. A.A.A.S., 1909 p. 262. 



