122 Secondary Beds of Northern Australia. 



bed of dry white sand and gravel, with water-holes at 

 uncertain intervals, more frequently found in some of the 

 ana-branches than in the main channels ; but water may 

 generally be procured by sinking wells in the sandy beds 

 of the larger rivers. 



The tributary creeks have much the same character on a 

 smaller scale ; but in these the timber is confined to a single 

 line round the water-holes, and the plains are for the most 

 part treeless. 



After heavy storms a torrent may roll down these water- 

 courses for a few days, but when the rain ceases they soon 

 resume their usual arid appearance. 



The soil is sandy and loose, rising up in a spongy mass in 

 wet weather, when many parts of the plains become nearly 

 impassable, and in dry weather opening in innumerable 

 fissures. Miles of country may be ridden over without 

 seeing a square yard of unbroken surface. This character 

 will of course be greatly modified as the surface is trodden 

 firm by stock. 



In all the sections observed, the underlaying formation 

 was a fine-grained sandstone in horizontal beds, apparently 

 undisturbed. Flattened nodules of limestone, often enclosing 

 fossil shells, were scattered about the surface in many places' ; 

 but no limestone beds were seen. 



Cretaceous shells were picked up on the Flinders River, 

 near the centre of the plains, and near the junction of the 

 horizontal sandstone beds with the rocks of the M'Kinlay 

 ranges. 



The place where the bones of the ichthyosaurus and 

 pleisiosaurus were found is on the point of a low rise 

 bounding the flats of the Flinders River, and about six 

 miles from its present channel. Here we have the same 

 sandstone formation in horizontal beds ; but the saurian 

 bones, and most of the shells, were found on the surface of 

 the soil. The first discoverer of one of the saurians 

 described it to me as presenting the exact appearance of an 

 animal, whose body had decayed on the surface, leaving the 

 skeleton on the grass. The singular position in which these 

 shells and bones are found is evidently owing to the friable 

 nature of the sandstone in which they have been enclosed-; 

 the slow disintegration and gradual removal of this rock 

 having at length left the harder fossils on the surface. 



In some places where the rock was exposed the apparently 

 hard stones crumbled to pieces in the hand, indicating the 



