GEOLOGICAL SOCIETY OF DUBLIN. 



135 



WEDNESDAY EVENING, APRIL 8, 1857. 

 D. M'Causland, Esq., in the Chair. 

 Mr. R. Geiffiths read the following — 



NOTES EXPLANATORY OF THE SUBDIVISIONS OF THE CAEBONIFEEOUS SYSTEM, 

 AS LAID DOWN ON HIS LAEGE " GEOLOGICAL MAP OF IEELAND," AND 

 EXEMPLIFIED IN THE SECTIONS ENGEAVED ON THE MAEGIN OF THAT MAP, 

 AS ALSO IN OTHEES EXHIBITED AT SEVEEAL MEETINGS OF THE BEITISH 

 ASSOCIATION FOE THE ADVANCEMENT OF SCIENCE, DUEING THE LAST 

 TWENTY YEAES. 



In the infancy of the science of Geology geologists were in the habit of 

 grouping rocks which presented some character or characters which were 

 common to all the members of a general system. Thus my lamented 

 friend, Greenough, in the first edition of his " Geological Map of Eng- 

 land," coloured the entire Carboniferous System of England with a light 

 shade of black ; but as careful and minute observation extended, he found 

 it necessary to subdivide the system into four members, namely, Lower 

 Limestone, Upper Limestone, Millstone Grit, and Coal. 



A similar process gradually took place in the colouring of my "Geo- 

 logical Map of Ireland," the first outline of which was exhibited by me 

 in the year 1813 ; and these gradual changes have not been confined to 

 the Carboniferous, but extended gradually to the older sedimentary as 

 well as the igneous rocks, each being introduced so as to correspond with 

 the development of geological science, much exertion having been made 

 by me to keep pace with modern discoveries and views, and with subdi- 

 visions based as well on stratigraphical as on palseontological data ; and 

 although in some localities the accuracy of the lines of division adopted by 

 me, particularly those between the Old Eed Sandstone and the Yellow 

 Sandstone in the north, and between the Silurian and the Old Red Sand- 

 stone in the counties of Cork and Kerry, may be liable to further consi- 

 deration, and perhaps may still admit of modifications in doubtful cases, 

 I have yet the satisfaction of believing that the last edition of my 

 " Geological Map" corresponds with the views generally entertained by 

 our most accomplished and experienced practical geologists. 



This short history of my geological proceedings is made at the present 

 time in consequence of the paper read by Mr. John Kelly at the meet- 

 ings of the Society for the months of January and March, in which he 

 endeavours to impugn the accuracy of the subdivision of the Carbonife- 

 rous System of Ireland which has been adopted by me for upwards of 

 twenty years. 



Previously to that period, in conformity with the principle adopted 

 by Mr. Greenough and others, the Carboniferous System of Ireland was 

 represented on my " Geological Map" by two colours, — blue and black, — 

 the first representing the limestone, and the black the Coal series ; but 

 during the progress of my geological observations, made as opportunity 

 offered in every part of the country, I found that, although my original 



