Physiography of Bulla Area. 329' 



lateral displacement must have taken place, and, though this is the 

 probable explanation, yet local lenticular accumulations of con- 

 glomerate may be the reason why these bands do not appear on the 

 same line of strike. Owing to intense pressure, well defined joint 

 planes have been set up which tend to break the strata into small 

 rhomlx)hedra. These joint planes give difficulty in the taking of 

 dips and strikes, as they closely simulate the bedding planes. 



Palaeozoic Fossils. — Previous to 1918. Upper Ordovician grap- 

 tolites had been found in the extreme north-west of this area (4), 

 while Lower Silurian graptolites had been found in the extreme 

 south-east (5), but none had been found between these localities. 



In 1917 and 1918 the writer came across several fossil beds whose 

 position is indicated on Plate XXXII. The paucity of fossils in this 

 locality is probably due partly to dynamic and thermal meta- 

 morpliism, which prevent the rock splitting along the bedding plane, 

 and partly to the sandy nature of the sediments. 



It has been suggested that the conglomerate C, is of glacial 

 origin, and the absence of fossils in this neighbourhood is due 

 to the severe climatic conditions that prevailed during their 

 deposition. (6.) Fossils have, hoAvever, now been found in the 

 following localities : — 



(a) On the left bank of Jackson's Creek, 50 yards north of 



the mouth of Column Gully. (See Plate XXXII.) In a 

 very narrow band Upper Ordovician graptolites can be 

 obtained in abundance. Coenograptus and Diplograptus 

 being the commonest genera. The fossils are well pre- 

 served, but are rapidly obliterated on exposure to the air. 



(b) On the left bank of Jackson's Creek, half a mile south- 



east of the Organ Pipes. For nearly a mile along both 

 banks of tlie creek, the rocks contain enormous numbers 

 of worm impressions. On the rook face a few yards south- 

 east of dvke D the markings stronglv suggest worm 

 burrows, but Mr. F. Chapman says that they are probably 

 the remains of the soft part of the worms. The impres- 

 fiions are quite different from > those of Trachyderma (7). 

 From the graptolite bed referred to in (a) to the con- 

 glomerate C these impressions occur in varying num- 

 bers. The upper part of eacli stratum has more im- 

 pressions than the lower part, and many of the most 

 prominent markings are perpendicular to the l:>edding^ 

 plane, and increase in diameter from below upwards^ 



