48 L. F. Harper — Evidence of Uplift. 



Art. III. — Evidence of Uplift on the Coast of New South 

 Wales, Australia ; bj L. F. Harper. 



During a ^eolo^ical survey of the Southern Coal Field of 

 New South Wales, evidences of an uplift of a portion of the 

 coastal belt of that State were studied. 



The coastal plateau of the Illawarra district is formed of 

 Permo-Carboniferous and Triassic strata capped by the resist- 

 ant Hawkesbury sandstone. Contemporaneous lava flows are 

 included in the series, and sediments aud lavas alike are 

 intruded by dikes of basaltic rock, chiefly monchiquite and 

 camptonite. The dip of the strata is northerly, parallel with 

 the coast line, and vigorous wave erosion on the plateau edge 

 has formed long lines of sheer cliffs in Triassic sandstone and 

 clifled headlands interspersed with shingly beaches in Permian 

 beds and lavas. ^ 



In the Illawarra district each rock headland is faced by a 

 flat rock shelf, the surface of which is developed generally on 

 a stratification plane. These shelves vary in width from 70 to 

 250 feet and stand 2 to 4 feet above high-water. They are 

 most pronounced on headlands where a dense lava flow over- 

 lies sedimentary strata. Vertical dikes crossing the shelf are 

 less resistant to weathering than their bordering walls and are 

 usually represented by open channels at sea-level or by fissures 

 in the clift' face. (Fig. 1.) 



At three localities in the neighborhood of Kiama, so-called 

 blowholes are found. These are openings into the clifl face at 

 sea-level and. consist either of a horizontal tunnel with an out- 

 let vertical to the land surface, or of a tunnel only. In the 

 case of the former, the water propelled by waves passes 

 through the tunnel and escapes by the funnel-like, vertical 

 opening as a shower of spray. Two blowholes with vertical 

 outlets were noted. Although both occur in the same contem- 

 poraneous lava flow, each has a separate origin. 



The principal Kiama blowhole was produced by the action 

 of the sea on a decomposed dike in the lava. A tunnel about 

 60 feet long resulted. Owing to a depression of the land sur- 

 face, the sea formed a vertical opening at the landward end of 

 the tunnel, up which the spray is driven to a considerable 

 height. (Figs. 2 and 3.) 



In places, the lava flow is columnar and rests on a bed of 

 volcanic tuff — factors leading to the formation of a second type 



* For a description of tlie geology of this region see: — Harper, L. F,, 

 Geology and mineral resources of the Southern Coal Field, Memoirs Gaol. 

 Survey New South Wales, Geology No. ?, Sydney, New South Wales, 1915. 



