1198 NOTES ON THE GEOLOGY OF BOWNING, N.S.W., 



srood fossils. The limestone is of a nodular character. This 

 feature may have been caused by the presence of fine non-calcareous 

 silt, which filled the spaces between the corals, and prevented their 

 cohesion. This zone is rich in brachiopods and gasteropods. Of 

 crustaceans I have obtained fragments of two trilobites, Cheirurus, 

 sp., and Cromus Beaumonti. Among the brachiopods are the 

 familiar Upper Silurian species Atrypa reticularis, Pentamerus 

 oblongus ; also, remarkable above others, is a deeply corrugated 

 Pentamerus of triangular shape, that 1 have not yet identified, and 

 which appears to be typical of this zone. The dip is from 30° to 

 40°, and its direction S. of W. The whole thickness may be 

 estimated at 125 ft. 



The upper portion of the bed is thicker and more compact. 

 During its growth the invasions of silt had ceased, and corals and 

 molluscs increased without hindrance except for the antagonism 

 that may have prevailed among the different forms of life. The 

 characteristic fossil, not coralline, is the large Euomphalus Clarkei, 

 A very large / entamerus also occurs. The dip is less than in the 

 lower division and ranges from 15° to 20°. The upper division 

 has a thickness of about 200 feet, so that the total thickness of 

 the bed, therefore, may be fixed at 300 feet. Further south, 

 however, at the Humewood beds of Mr. Jenkins's paper, it attains 

 greater thickness. It may not be out of place to remark here 

 that the general strike of the bed agrees well with the trend of 

 our present coast-line. From this fact the obvious conclusion to 

 be drawn is that our ancient coast-line had a similar trend. 



Passing westward we advance to the next bed. Here we have 

 presented the evidence of a great and sudden change in the 

 ancient physical features. The clear sea became densely charged 

 with fine sediment, which established the beginning of the end of 

 the coral reef just referred to. 



This bed not only introduces a great change in the character of 

 the rocks, but a sweeping change of fauna. From this upward most 

 of the large molluscs disappear to be seen no more throughout the 

 series. Corals, encrinite stems, and some brachiopods are found in 

 the lower part of the bed. 



