OF NEW SOUTH WALES. 25 



The chief fossils obtained from this rock were several species 

 of Spirifer and Atrypa, including Atrypa reticularis, and A. 

 aspera — a Stroplior}iena (dorsal valve convex), a Bellerophon, 

 Eimema, Bcculiompliulus, Maclurea, and a large Helix-like 

 Trochus. Among the Conchifers, a large Area-like species is the 

 most conspicuoas. Of Trilobites ; Phacops, and Gromus. This 

 limestone, at Mylora, is overlay ed by a flaggy unfossiliferous 

 limestone. The whole thickness of the Yass Beds, near Yass, is 

 about 1,000 feet. Dip from 30° to 40° lower division. Dip 

 from 18° to 40° upper division. 



We will now stop in our progress across the strata, and turn 

 aside a little to the south. Near one of the lower limestone 

 courses, beyond the town, I have obtained some very small 

 fossils that help to connect together the different parts of the 

 Yass Beds, and the Yass with the Hume Beds. A head of a 

 small sized Bronteus was found here. Peculiar to this spot is a 

 small, spherical, tuberculated Glabella, having a very Devonian 

 aspect. 



Hume Beds. 



Crossing now the Porphyry, separating the Yass and Hume 

 Beds, and starting from where the latter cross the Yass River, 

 and following the westward course of the river to a steep cliff, 

 then continuing in nearly the same direction across the beds, we 

 shall take the strata as before in the order in which they were 

 laid down. 



These beds are naturally divided into four parts, which division 

 will answer our present purpose well enough. The first, from the 

 Porphyry to the river at the base of the cliff, near the junction of 

 Boonu Ponds with the Yass River ; the second, from the river to 

 the top of the Coral Reef; the third, from the Coral Reef to the 

 Trilobite Limestone ; in the fourth, I have not as yet found any 

 fossils. We have first some laminated Porphyry, in which are 

 various fossils, among others encrinital stems of a Lower Silurian 

 type ; then a limestone, more developed and richer in fossils, at 

 the Derringullen and Limestone Creeks ; then a mass of 

 sub-crystalline altered rock, traversed in one place by igneous 



