196 



Again the intermediate formation, the Nowra Grits, 

 displays great differences from both of the other formations, 

 and evidently a great change in conditions took place, which 

 caused both an alteration in the nature of the sediments, 

 and in their fossil contents. The Nowra Grits really 

 represent a temporary break, which has interrupted what 

 wonld otherwise be continuity of conditions from the 

 Wandrawandian to the Gerringong period, with the resulting 

 production of one comparatively uniform formation. 



For instance, the W;indni\v;uidian Series were laid down 

 during a steady period of subsidence, the rate of which 

 corresponding approximately with the rate of sedimentation 

 kept conditions uniform. During the deposition, however, 

 of the Nowra Grits, a sudden check of this subsidence, with 

 possibly in some places a slight elevation, altered conditions 

 materially. Portions of the sea-bottom were probably 

 again elevated above sea level, and brought within the 

 action of the breakers and of atmospheric agencies, so 

 that the neighbouring sediments became coarser, and sub- 

 sidence having ceased, the sea became rapidly shallow. 

 That, this was the case can be seen by the fact that false 

 bedding is exceedingly common in the Nowra Grits. The 

 fauna also had changed, the abundant and varied forms of 

 the Wandrawandian Series having either died off, or 

 migrated to more congenial surroundings, and only the 

 more common forms of brachiopods, which evidently stood 

 a wider range of conditions than the more highly differen- 

 tiated pelecypods still remained. Fossil wood is sometimes 

 met with in the Nowra Grits, one piece found at Longreach 

 consisting of a thin carbonaceous film, lying on the bedding 

 plane, and over a foot in length by about 2! inches across. 

 'I'll is shows that the shore line at this time was evidently 

 nut far distant. 



Again, however, subsidence took place, and on the 

 resumption of old conditions, nearly all the same fauna 



