LV.—ANNIVERSARY ADDRESS TO THE ROYAL GEO. 
LOGICAL SOCIETY OF IRELAND, psy G. H. KINAHAN, 
M.R.I.A., President. 
[Read February 16th, 1880. ] 
THE past year has been one of considerable activity in our 
Society ; but I do not propose to give now a resumé of our 
proceedings. I cannot, however, pass, without mention, the fact 
that, in accordance with the proposal that an annual geological 
excursion should form part of the programme of the Society, such 
an excursion was organized last summer to Ovoca, a very eligible 
geological locality. It was attended by a goodly number of 
Fellows and their friends, including several ladies, and, with the 
exception of a slight temporary interference on the part of the 
weather, everything passed off well, and apparently to the satis- 
faction of all the company. 
Instead, then, of giving, in this Anniversary Address, a review 
of the papers read before the Society during the last twelve 
months, | would direct the attention of Fellows to the following 
subject of general interest to geologists, viz.:—The system, which 
is at present too prevalent, of estimating the Thicknesses of 
Geological Formations. 
To estimate, with approximate correctness, the thickness of a 
formation, is often, and in various ways which need not be pointed 
out, a very important problem in geology ; and, if it is wrongly 
done, serious ulterior error may be the result. It seems to me to 
be frequently the case, at present, that incorrect conclusions are 
drawn respecting this matter, and that the different groups or 
formations are usually made to appear of greater than their true 
thicknesses. 
The presentations of a formation in different districts are too 
often taken as if they were similar to different copies of the same 
book ; and if some sub-group which appears in one place is not 
present in another, its absence in the latter is regarded as a 
hiatus which ought to be filled up with a supposititious group of 
