Anniversary Address to the Royal Geological Society. 487 
regards the present question, in the vicinity of more or less 
distinct sources of material, similarly to what is going on at 
the present day. The fact of the accumulation in more or less 
separate basins of the materials of various formations has been 
contended for by Dr. A. C. Ramsay, and more recently it has 
been prominently brought forward by Dr. Archibald Geikie, in 
his paper on the “Old Red Sandstone of Western Europe.”* 
From my own observations in Ireland I have been gradually 
led to a similar conclusion respecting each of the Irish rock- 
formations. These, from the Cambrian to the Miocene, apparently 
consist of somewhat separate basin-accumulations ; and the real 
thickness of the groups seems to be less than what is usually 
supposed. 
In many cases, no doubt, it is unwarrantable to argue from 
small to great things; but in that which I am now considering, 
this is not so; in it the difference of scale cannot affect the prin- 
ciples involved, nor the mode of the operations. If, then, in 
legitimate illustration of the present point, we examine a recent 
lake-accumulation, we often find in one part shingle, in another 
gravel or sand, elsewhere marl or clay, or perhaps peat; and if 
circumstances allow a section to be cut across the deposits, the 
shingle, gravel, and sands will nearly always be found dipping at 
greater or less angles, the clays and peat being more or less nearly 
horizontal, while the marl may have different characters in differ- 
ent places, according as it has been mechanically or chemically 
formed. 
If the thickness of the accumulation, as a whole, is calculated 
by adding together those of all the layers of different composition, 
a much greater thickness will often be arrived at than that which 
would be possible, even if the depth of the whole lake were greater 
than its present maximum. I have seen a small lake basin, 
the accumulations of which would, if thus treated, give a thick- 
ness of over 100 feet, although in no place was the original lake 
more than 20 feet deep. In large lake basins the results would 
probably be much more striking. 
If trom lake basin deposits we go to those accumulating at 
the present time in the Atlantic Ocean, we also find deposits of 
shingle, gravel, sand, clays, peat, &c., going on in different places ; 
* Trans. Roy. Soc. Edinb., vol. xxviii. 
