Mr. Weaver on the Structure of the South of Ireland^ Src. 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. 071 the Mineral Structure of the South of Ireland, mith 

 correlative matter on Devo7i and Cornwall, Belgium, the 

 Eifel, Sfc. By Thomas Weaver, Esq., F.B.S., F.G.S., 

 M.B.I.J., ^c. Si-c. 



[Continued from p. 404, and concluded.] 



POSTSCBIPT. 



CINCE 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 unconformahly 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- 



* Lond. andEdinb. Phil. Mag. for March 1840, with a plan and two 

 sections. 



