1862,] 



HAUGHTON GRANITES OF IRELAND. 



405 



The joint-planes east of north are confined to the district around 

 Sheskina-roan, Meen Bannad, and Anagarry, which is limited in 

 extent, as compared Avith the entire district examined. 



The following Table shows the arrangement of the observed 

 eleavage-planes, according as they were found to lie south or north 

 of west. 



Table III. — Cleavage- or Stratification-planes in the Granite of 



1 South of West (B'). 



North of West (B'). 



Secondary (C). 



1 10° 



15 



10 







10° 



30° S of W. 



' 8° 45' S. of W. 



10° N. of W. 



30° S. of W. 



Mean =5° S. of W. 





Neglecting the secondary planes of structure, which have not been 

 as yet sufficiently observed to found any statement upon, it would 

 appear, that in the granite of Donegal there is one system of Con- 

 jugate* planes, having the following direction : — 



Cleavage B'. 



Joints B. 



Angle. 



5°0'S. ofW. 



3°4'W. ofN. 



88°4']Sr.toK 



The magnetic variation in the part of Donegal examined was 

 2&^ 40' W. Applying this correction to the preceding results, we 

 find in true bearings — 



B'. Cleavage-planes 31° 40' S. of W. or N. of E. 



B. Joint-planes 29° 44' W. of N. or E. of S. 



In the Co. Waterford I succeeded in establishing the existence 

 of four conjugate systems, the most prominent of which is found in 

 Donegal only as a secondary system — viz. 33° 31' N. of E. (mag.). 



The conjugate system in Waterford, which is second in import- 

 ance, rests upon 130 observations, and is nearly coincident with the 

 most prominent system of Donegal, viz. — 



B'=7° 46' N. of E. (mag.) =32° 26' N. of E. (true). 

 B =6° 57' W. of N. (mag.) = 31° 37' W. of N. (true). 



In making the reduction from magnetical to true bearings, the 

 variation in the south of Waterford is assumed to be 24° 40' W. 

 It will be observed that the geographical axis of the Donegal 



* For the definition of this term, and an account of the conjugate systems ot 

 cleavage- and joint-planes in the Old Eed Sandstone of the Co. Waterford, see^ 

 the Author's paper pubHshed in the Phil. Trans, vol. cxlviii. p. 333, 1858. 



2e2 



