1 74 Succession of the Older Stratified Rocks in Ireland, 
“ that all those tracts which occur between Dublin and Dun- 
dalk, along the course of the Boyne, and in the hills separa- 
ting the counties of Cavan and Meath, which have been de- 
scribed as the older graywacke or transition series by Mr. 
Griffith, Mr. Weaver, and others, are in reality all conform- 
able, and immediately inferior to the mountain limestone and 
superior to the old red sandstone, and consequently belong 
to the Devonian seriesc” 
I confess I am surprised at the view here taken by Mr. 
Hamilton, as one of the facts on which his argument is 
grounded, namely, that the rocks coloured by me as transition 
are superior to the old red sandstone, have been correctly 
stated by himself* to be inferior to that rock where it occurs 
near Balriggan mill, N.W. of Dundalk, in the county of 
Louth, in which locality the old red sandstone rests uncon- 
formably on the transition slate. 
In regard to the second point, namely, that the schistose 
rocks are succeeded by the limestone in a conformable posi- 
tion, I have to observe that such is not the fact; for in the 
only localities in which 1 have been hitherto enabled to ob- 
serve the contact of the tw^o rocks, the limestone rests uncon- 
formably on the transition slate. These localities are in 
the river north-east of the Naul, in the county of Dublin ; 
at the southern extremity of the village of Duleek, in the 
county of Meath ; at Old Bridge on the banks of the Boyne, 
two miles west of Drogheda, in the county of Louth ; and at 
Headfort near Kello, in the county of Meath. 
Fortunately, in addition to these facts, we have also another, 
which is quite conclusive, namely, the discovery of fossils 
belonging to the lower Silurian rocks or Caradoc sandstone, 
which occur in considerable abundance at Grangegeeth, four 
miles north of Slane, in the county of Meath : the fossils have 
recently been examined by Mr. Murchison and Mr. Lonsdale, 
of the Geological Society of London, to whom 1 had sent 
them, and both are of opinion that they belong to the lower 
Silurian rocks f. Consequently we must come to the conclu- 
sion that Mr. Hamilton’s opinion is erroneous in respect to 
the geological position of the slate district, north of Dublin, 
and of that between Drogheda and Dundalk. 
I have now replied to all the important observations con- 
tained in Mr. Hamilton’s paper, which tend to cast a doubt on 
the accuracy of my Geological map, and I think I have been 
* See Journal of the Geological Society of Dublin, vol. ii. part i. 
f The fossils found, and which have been compared with the original 
Silurian forms collected by Mr. Murchison, are Orthis semicircularis and 
Orthis virgata ; in addition to which there are several other forms of the 
genus Orthis which have not as yet been clearly identified, 
