104 Commentary on 



" species, we find so extraordinary and unexpected an amount 

 " of agreement between these beds and the similar shales, 

 '^ sandstones, and impure limestones forming the base of the 

 " carboniferous system in Ireland, that it is impossible not to 

 " believe them to be nearly on the same parallel; and there is 

 " equal difficulty in imagining them to be either younger or 

 " older than those deposits. Of those species no less than 11 

 " are believed to be positively identical, on the most careful 

 " comparison of the Australian and Irish specimens; and nine 

 " more are so closely allied that it has been found impossible 

 '^'^to detect any difference of character, as, either from 

 '^imperfect preservation or want of sufficient specimens to 

 '' display, all the characters have not been specifically iden- 

 *' tified. With such e^ddence as I have mentioned, I do not 

 " think it improbable that a wide geological interval occurred 

 "between the consolidation of the fossiliferous beds which 

 " underlie the coal, and the deposition of the coal measures 

 " themselves; that there is no real connection between them, 

 " but that they belong to widely different geological systems, 

 " the former referable to the base of the carboniferous system, 

 " the latter to the oolitic, and neither showing the slightest 

 " tendency to a confusion of type/^ 



Since the above was written, Mr. Dana, who in 1839 

 published his observations, with the American Exploration 

 Expedition, visited the localities, and got several more 

 fossils, without causing any alteration in the above views ; 

 and a few years ago Mr. Selwyn, the director of the Victorian 

 Geological Survey, made an official survey of the Tasmanian 

 coal-fields, in which Count Strzelecki thought the clays con- 

 taining large shells of the genus Pachydomus, such as are 

 found under the coal-beds at Newcastle, seemed doubtfully to 

 overlie the coal-beds of Tasmania, which would thus be 

 proved to be of the same age as the underlying palaeozoic 

 shell-beds. Mr. Selwyn found the Pachydomus beds, how- 

 ever, all in their true normal position, under the coal 

 everywhere in Tasmania as in New South Wales, thus 

 clearing away the only even doubtfully suggested strati- 

 graphical objection to my views. It may also be satisfactory 

 for me to state that all the information I have been able to 

 acquire, for the last twelve years, bearing on the question, and 

 derived from N. S. Wales, Victoria, or Tasmania, stratigraphi- 

 cal as well as palseontological, tends to confirm my original 

 impression above quoted, and that I know of no fact invalida- 

 ting it, or which, in fairness, I could state on the other side. 



