384 W. K. BROWNE AND A. B. WALKOM. 



and at the plain level on the eastern side, is undoubted 

 evidence of local vertical movement. This fault, the more 

 easterly of the two, is the older. Two other small and 

 doubtful faults are shown on the map, at Post Office Hill, 

 and at the place named Jerusalem Rock. In both cases 

 the throw is probably small and the evidence for the fault- 

 ing is mainly physiographic, showing that such faults, if 

 they really exist, are of comparatively recent origin. 



Other faults, postulated on geological grounds and noted 

 on the map, will be referred to as they occur, in dealing 

 with the general geology of the district. 



Geological Age of the Formations. 



In this district there are representatives of two, and 

 possibly three, geological periods. The principal and most 

 interesting series, comprising acid, intermediate and basic 

 lavas, is of Carboniferous age : in the Lower Marine of the 

 Permo-Oarboniferous, basic lavas and tuffs are developed : 

 while underlying the Carboniferous lavas of Mount Bright 

 is a long narrow outcrop of grano-diorite which is either 

 Lower Carboniferous or Pre-Oarboniferous. It is with the 

 Carboniferous lavas that we are chiefly concerned in this 

 paper. 



Round the gently sloping elevations comprised in the 

 Drake's Hill area the basal conglomerates and sandstones 

 of the Lower Marine can be traced in such a way as to 

 leave no doubt that they actually surround it. They appear 

 dipping at a low angle off the igneous rocks, so that it may 

 be concluded that Drake's Hill was an isolated elevation 

 on the floor of the Permo-Oarboniferous sea, against the 

 sides of which these sediments were deposited. This con- 

 glomerate contains pebbles of the rocks of which the inlier 

 itself is composed, so that the eruptives are anterior in age 

 to the Permo-Oarboniferous. The age of the Matthews' 



