762 GEOLOGY OF THE NORTH-WEST COAST OF TASMANIA, 



by Mr. Twelvetrees,* who quotes Rosenbusch's definition of the 

 rock as trachydolerite, and notes it as being quite distinct from 

 the ordinary olivine basalt of the coast, and the product of a 

 different magma.] 



Table Cape to River Detention. (Plate xxviii.). 

 From Table Cape westward the rough bridle track, the only 

 land route to Circular Head, keeps along the edge of a great 

 basaltic sheet for the next five miles at an elevation of from 200 

 to 400 feet above the shore-line. Jt is much obstructed by scrub 

 and fallen timber, being very seldom travelled by any one. 

 Whether there are outcrops of the ancient rocks below the basalt 

 it is hard to say, the steep descent clothed with dense scrub 

 preventing access to the beach. Approaching Jacob's Boat 

 Harbour the track descends abruptly to a sandy beach. Here 

 are bands of quartzite with adherent conglomerate of waterworn 

 and subangular pebbles, both rocks being traversed by small 

 quartz veins. The low point half-a-mile farther west, which 

 protects a landing place, is also of quartzite dipping at 25° 

 N.N.E. At the junction of the point with the shore are strong 

 bands of quartzite nearly vertical and striking east and west,, 

 and there is a patch of a dark-coloured flat-bedded conglomerate 

 of small pebbles. From Boat Harbour the track climbs steeply 

 towards Sisters Hills, a lofty range of massive quartzite, passing 

 near some thin patches of outlying basalt. This quartzite occupies 

 the whole of the rugged country westward for the next seven miles 

 except near the mouth of Sisters Creek. The coast-line at Sisters 

 Hills is bounded by steep cliffs rising abruptly from the water's 

 edge. The descent to the Sisters beach is very steep, the so-called 

 track being encumbered with loose sliding rocks, and the ups 

 and downs for the next few miles over the Rocky Cape Range 

 are much of the same description. The Sisters Creek emerging 

 from a rocky gorge crosses a belt of low sand dunes and quartz 

 gravel, and for about a mile east and the same distance west of 



*" Trachydolerite in Tasmania." By W. H. Twelvetrees, F.G.S., Govern- 

 ment Geologist. 



