Mr. Weaver on the Structure of the South of Ireland^ ^c, 471 
The spec. grav. of Isle of Wight sand at 64° Fahrenheit was 
2*64<4. The spec. grav. of crown window glass (as made at 
Nailsea,) is 2*532. Its ingredients are sand, soda, and lime. 
Now, if we leave the silex a constant quantity, how is it 
that any increase of lime, or of soda, increases the specific 
gravity of the resulting glass ? 
Any addition of alumina will produce the same effect. 
In mentioning an increase of lime, or of soda, or of alu- 
mina, I mean of course, an increase beyond the usual pro- 
portions of each ingredient commonly employed. 
I have the honour to remain. 
Gentlemen, yours, &c. 
Wraxall, near Bristol, CHARLES ThorntoN CoATHUPE. 
March 4, 1840. 
LXX. On the Mineral Structure of the South of Ireland^ *with 
correlative matter on Devon and Cornvoall^ Belgium^ the 
Eifel^ ^c. By Thomas Weaver, Esq.^ F,B,S,^ F,G.S,, 
M,R.LA,, ^c, 8^c, 
[Continued from p. 404, and concluded.] 
POSTSCRIPT, 
QINCE the preceding pages were committed to the press, a 
^ paper by Mr. Griffith, entitled On the True Order and 
Succession of the Older Stratified Rocks in the neighbour- 
hood of Killarney and to the north of Dublin^,” has reached 
my hands. In reference to the vicinage of Killarney, I feel 
it incumbent on me to offer a few remarks. 
I think it unfortunate that Mr. Griffith should persevere in 
placing in the same parallel, and designating by the same 
name, two series of strata which by his own showing are 
clearly in a different order and in a different position ; thus 
pursuing the same course in Kerry as in Waterford, alike 
productive of obscurity and confusion, by a misapplication of 
the term old red sandstone.’’ Thus this formation, which 
is so well characterized in the Slieve Meesh range (Cahir- 
conree of Mr. Griffith), by its peculiar beds, horizontal dis- 
position, and in overlying unconformably the older stratified 
rocks situated on the west (which latter generally approach 
the vertical position), is placed in parallel with those beds of 
conglomerate, sandstone, quartz-rock (greywacke), and clay- 
slate, occasionally coloured of a reddish hue, which form 
incidentally intercalated conformable portions of the consecu- 
* Loud. andEdinb. Phil. Mag. for March 1840, with a plan and two 
sections. 
