98 Commentary on 



genus " to agree in all things with the typical characters of 

 the genus ;^^ — this would require nearly as many genera as 

 species, and destroy the advantages of the larger groups. The 

 accepted rule might be roughly exemplified thus : If a genus be 

 characterised by three positive characters, one of them may 

 vary in any species which, possessing the other two unaltered, 

 might be classed with the given genus ; but different species 

 would not necessarily vary in the same character. Apart 

 from this general illustration, I may observe that the generic 

 references of the Australian fossil plants have never been 

 objected to by botanists, and they have all been carefully 

 made by observers (except myself) of universally acknow- 

 ledged accuracy. 3rd. As for the objection that the plant 

 beds cannot be oolitic, because no oolitic animal remains have 

 been found, there is nothing in it ; for at Richmond, in Vir- 

 ginia, there is a coal-field twenty miles long, with beds of 

 coal forty feet thick, worked by shafts one thousand feet 

 deep, the coal-beds, accompanied by layers of fossil plants, 

 having a strong general resemblance to those of the New 

 South Wales coal deposits, the whole series being, after de- 

 liberate sm^vey and examination (amongst others by Sir 

 Charles Lyell and Professor Eogers), distinctly and unani- 

 mously referred to the oolite * formation by all the geologists 

 and palseontologists of America and Europe ; and yet, in the 

 whole of North America, though more fully examined than 

 New South Wales by geological surveyors, not a trace has 

 yet been found of any oolitic zoological fossil. 



Mr. Clarke's next paragraph says, " The two genera, 

 " Tceniopteris and Glossopteris {SagenojJteris) have been the 

 " means of placing, by some geologists, the coal deposits of 

 '' Australia and India in the horizon of the oolitic coal. Now, 

 " the latter occurs in five distinct formations in India, as Mr. 

 '' Oldham informs me, and it also occurs in Africa, where the 

 " evidence appears to be against the supposed epoch.'' This 

 paragraph shows that Mr. Clarke has missed some important 

 links in the chain of reasoning by which I considered the coal 

 rocks of the Hunter related in geologic age to the oolitic forma- 

 tion. I rarely take the liberty, in any paper of mine, of stating 



* Very recently the suggestion has been discussed of the " Triassic " age 

 of these American beds, but the e\'idence is inconckisive, and at farthest the 

 trias is as much mesozoic as the oolites, and the discussion in question would 

 not help Mr. Clarke's position of his Newcastle plant-beds being of the 

 Pieljeozoic Carboniferous age of the imderlying marine-beds with Trilobites, 

 nor invalidate my view of their mesozoic character. 



