BY C. JENKINS, L.S. 407 



depths. But there is evidence that they were laid down in shallow 

 seas, during alternate sinking and rising of the land, sometimes 

 in an open sea, and sometimes in salt-water lagoons, while some 

 were evidently exposed during deposition, to the action of the 

 sun and wind. This evidence is afforded by the nature of the 

 rocks as well as by the mode of occurrence and condition of the 

 fossils. 



The depth required for the formation of shale, such as these 

 beds contain, according to Dana, need not be more than a few 

 hundred feet. 



The compact Limestone and Coral conglomerates, are such as 

 Dana describes as now forming in the Coral Islands, and would 

 not be produced at depths exceeding 200 feet. 



The grits with their ripple marks, and the bands of Limestone 

 with sea-weed, all tell of shallow seas. The beds of unfossilif erous 

 shale, some finely laminated, such as could only be formed in 

 quiet water, and capable of retaining the slightest impression, 

 together with the brackish springs flowing from them, afford 

 evidence similar to that which eminent geologists have agreed to 

 consider, as indicating that the beds so characterised, were 

 deposited in salt-water lagoons only occasionally in communication 

 with the ocean, rather than in an open sea. Dana has shown 

 that such unfossilif erous deposits are now forming in some of the 

 lagoons of the Coral Islands. 



In the Yass beds especially, the mode of occurrence of the 

 fossils, generally in layers, almost universally broken, worn, and 

 sometimes so rolled as to be almost unrecognizable, show the 

 stratum containing them was during its deposition subject to the 

 action of the waves. Some of the fossils in the Hume beds exhibit 

 a similar mode of occurrence, but in general in these latter beds the 

 fossils are more evenly spread through the strata, and the perfect 

 condition in which these are found show that they were deposited 

 beyond the reach of tidal action. 



