270 Mr. Hamilton on Mr. Griffith's Paper 



The values of cp t c s, deduced from the observed values of 

 P l> s > gi ven by W. Phillips in his Mineralogy (third edition), 

 are 32 45' and 4-2 20'. My determination of these angles 

 differs only about two minutes from the former, and agrees 



Fig. 3. Fig. 4. 



exactly with the latter. Unfortunately the figures which 

 were intended to express the angles pp", ss" (" a on a over 

 summit = 90, c on c over summit = 109 47'") are very 

 erroneous, probably through some mistake in transcribing 

 them, for the errors (which remain uncorrected in the fourth 

 edition) are much too large to have been errors of observa- 

 tion. 



St. John's College, Aug. 31, 1840. W. H. MlLLER. 



XL. Note upon Mr. Griffith's Paper "upon the true Order of 

 Succession of the Older Stratified Rocks near Killarney and 

 Dublin" By CHARLES WILLIAM HAMILTON, F.G.S.$c.* 



r |^HERE are a few points in this paper to which I think 

 -* it necessary to reply. 



I brought forward the result of my own observations with 

 diffidence, because I felt that they had been few and imper- 

 fect ; but I think they are not useless, and that I have, as I 

 then hoped, " pointed out an interesting field of inquiry, and 

 helped to show that a large portion of Ireland is still a sub- 

 ject for Geological debate;" and besides, I am still convinced 

 that my observations, as far as they went, were not inaccurate, 

 as Mr. Griffith asserts, although his subsequent observations 

 may have shown that some of my conclusions were so. 



Mr. Griffith has represented the fault which is observable 

 at Brickeen Island (L. & E. Phil. Mag. vol. xvi. PI. 2. fig. 2.) 

 as involving an upcast of about three thousand fcet> and the 

 beds of chloritic slate, quartz-rock, and old red sandstone as 

 cropping out at a low angle on the south-eastern slopes of 

 Glena mountain, at the base of which the fault is to be seen. 



Now in this case I am thoroughly convinced that my re- 



* Communicated by the Author, 



