764 GEOLOGY OF THE NORTH-WEST COAST OF TASMANIA, 



In a bight a little to the north of this cave is a massive dyke of 

 the same type as those noted between Burnie and Cooey Creek- 

 Seen at half-tide it is 15 yards wide and lies between walls of 

 quartzite, striking a little north of east, and with a northerly dip 

 of about 60°. 



On the coast, near where the track strikes the Detention beach,, 

 are outcrops of quartz schist with a northerly strike, and hard 

 flaggy sandstones so traversed by a rude cleavage and jointing that 

 the directions of dip and strike are much obscured. The lower 

 parts of the western slopes of the range are covered with thick 

 sheets of drift sand and quartz gravel, succeeded by marshes 

 fringed on the coast-line by sand dunes. Half-a-mile up the 

 River Detention is a patch of basalt partly covered with recent 

 drift, and extending southward. Here the river is fordable at 

 half-tide if the traveller is too late to cross at the bar. 



This is not the place to discuss the question of the intimate 

 relationship between the flora of a country and the character of 

 its rock-formations, but it may be noted that the large-coned 

 Banksia, B. serrata, which is common on the slopes of the Blue 

 Mountains and elsewhere in N. S. Wales, is found in Tasmania 

 only on the barren and otherwise almost treeless uplands of 

 Sisters Hills and the Rocky Cape Range. Here it is associated 

 with the dwarf grass-tree (Xanthorrhcea minor). On the rocky 

 headlands of the coast which has been described, but never far 

 above high- water mark, may be found the rare so-called '• Native 

 Sandalwood " (Alyxia buxifolia), with the delicate scent of the 

 Tonquin bean. In the gorges and low down on the western 

 slopes of the range are belts and wide stretches of the Wire Scrub 

 (Bauera rubioides), the terror of West Country explorers, which 

 nowhere else in Northern Tasmania approaches so near to the 

 coast. The same may be said of the Button-grass (Gymnoschcenus 

 sphenocephalies), which occupies marshy flats among the hills. 



River Detention to Circular Head. (Plate xxviii.). 



On the west bank of the river are dark-coloured flaggy slates 

 striking about N.E. For the next eight miles the country is 



