170 On some Tertiary Rocks 



right up to the River Murray., and thence may be traced 

 westward (from the sea coast to about 100 miles inland) to 

 the foot of the great dividing range which runs north and 

 south from the bend of Lake Torrens to Cape Jarvis. On 

 the east of this range it may be traced right along the great 

 Australian Bight. Here it appears in tall white cliffs con- 

 taining fragments of coral, and its appearance led Captain 

 Flinders to believe that this portion of Australia was an up- 

 raised atoll, and that an inland sea would be found the other 

 side. The whole formation owes its origin to detritus from a 

 coral reef. The further north, and the warmer the latitude 

 into which it is traced, the more perfect the fauna become. 



The reason, therefore, that fossils are so broken and so 

 scarce at Portland Bay, is because the latitude was too cold 

 for the reef to have nourished there, so that all that are found 

 have been brought from a distance, and consequently broken 

 in the transit. However, many beautiful novelties in polyzoa 

 have been discovered by me in a very perfect state, and have 

 been duly forwarded to the Geological Society of London. I 

 propose to do no more in this paper than merely allude to 

 the formations ; and, therefore, will pass on to the next, after 

 observing that the formation is of the Eocene or Lower 

 Miocene period, and does not extend much to the eastward of 

 Portland Bay, unless perhaps at Port Fairy. A mere seam 

 is all that is found further east. 



Above this is a stratum of decomposed trap. This is con- 

 tinuous with the same deposit at Flagstaff Hill and the 

 basalt under Cape Grant. Probably it has flowed from a 

 sub-marine crater which, to all appearance, has existed very 

 near the Lawrence Rocks, for all around that locality a thick 

 stratum of trifa, enclosing fragments of scoriae, is found. 

 There is no coralline found above the trap ; but the crag im- 

 mediately succeeds. The manner in which it is decomposed 

 varies very much in different localities. Thus near the 

 Whalers' Bluff it is greyish white, coarsely granular, and pos- 

 sesses large concentric circles of oxide of iron. At Flagstaff 

 Hill not a trace of its former crystalline texture remains. It 

 is decomposed into a deep bed of red ferruginous clay. At 

 the Lawrence Rocks the lava is as white as the limestone. 

 It powders easily, and sometimes contains disseminated 

 crystals of mica and selenite. 



At Cape Grant the line of junction between the trap and 

 the crag is not easily traced. The limestone from above has 

 been filtered down over the surface of the rock, so as to 



