32 THE PEOCEteDINGS OF THE LINNEAN SOCIETY 



and Hornblende, and probably Pyroxene. That some of these 

 rocks are newer than the sedimentary beds is evident by the 

 altered conditions of some of the strata in contact with them. 



Some may be of the same age, for in several places we have 

 the Porphyry enveloping fossils, while in others it is studded 

 with casts, which it has beautifully preserved, while it has 

 destroyed the shells. 



Of metals I will merely mention the fact that Galena has been 

 obtained in the Hume beds at Limestone Creek, near its junction 

 with the Derringullen, and near the Derringullen Creek, about 

 three miles from its junction with the Yass River. 



In comparing the fossils of these beds with those of the 

 upper Silurian of other countries, the absence of Graptolites 

 is a marked peculiarity. There are, however, abundance of 

 Bryozoan and probably Sertularian forms. It will also be 

 noticed that there are wanting those large forms of Cephalopoda 

 which are usually found in some of the beds of that age. 



This last fact seems of itself to point out how small a portion 

 the Yass Period represents of the Silurian of New South Wales, 

 and how impossible it would be to attempt to fix the exact 

 position of these beds in the Silurian series, until other beds of 

 the like age have been examined as carefully as these have been. 



Explanation of Plate VI. 



No. 1. — Phacops from the Limestone (Belle Vale Limestone), 



upper bed of 3 division Hume bed. 

 ,, 2. — Sprenochus from the Hume beds. 

 „ 3. — Fentamerus ohlongus. Hume beds, lower portion. 

 „ 4. — Galymene VuiMcata. Hume beds. (Lower Silurian, 



Europe). 

 „ 5 to 6. — Oheirurus. Hume Beds. 

 „ 7. — Oheirurus Insignis. Hume Beds. 



