148 



R. A. WEARNE AND W. G. WOOLNOUGH. 



4. Basalts. 

 Basalt intrudes and caps trachyte along the Main Divid- 

 ing Range near "The Gap." Basalt dykes intrude trachyte 

 at Mounts Greville, Edwards, French and Flinders. Basalt 

 dykes intrude andesite at Mount Alford, and basalt dykes 

 intrude rhyolite at Mount Barney. 



A striking difference is presented between the relation- 

 ship of the basalt dykes to the streams near the Main 

 Range and at Mount Barney. At the former locality the 

 dykes cross the streams at right angles, whereas at Mount 

 Barney the streams are subsequent and follow the course 

 of the dykes. Basalt seems to have been extruded through- 

 out the whole district by fissure flows. 



At the Main Range near Toowoomba two distinct dykes 

 of large dimensions can be seen along the eastern escarp- 

 ment — one at the 93 mile post on the railway line from 

 Brisbane, 200 yards in thickness, and the other at the 91 

 mile post exposing a width of 600 yards in the railway 

 cutting. Intrusive sills of basalt occur on the Main Range 

 along the old Warwick Road at an altitude of 2,040 feet, 

 and at the "Jump Up" see figs. 1 and 2. 



Fig. 2. 



w e: 



Sandstone 



i^Coal Seam 

 ^^•^^^T^^Basait Sill 



Rhyoiife Dyke 



Sandstone 



ftyolite Dyke 



Horizontal and Vertical Scale u 



j 10 Yards 



