482 



INTET7SIVE TUFF-LIKE EOCK.S IIS" IRELAND. [Aug. I9OI. 



The accompanying" map and sections (figs. 1-8) illustrate how 

 tuff-like rocks invade black slate of Llandeilo age, generally 

 adhering to the direction of bedding, but frequently cutting across 



it, and detaching 



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from the slate 

 numerous pieces. 

 These are more 

 numerous near the 

 margins of the in- 

 trusion than at a 

 distance, and re- 

 tain so distinct a 

 parallelism to the 

 margins that we 

 can only infer that 

 in some instances 

 there has been 

 no great movement 

 of the bounding 

 walls. 



Sometimes the 

 tuff-like rock con- 

 tains large, irregu- 

 lar masses, mostly 

 lenticular, as in 

 figs. 2 & 3. Some 

 of these masses are 

 themselves invaded 

 and almost severed 

 across by veins of 

 tuff-like material 

 projected from the 

 enclosing magma. 

 The section shown 

 in fig. 5 (p. 484) 

 is the bottom of 

 a cliff-face about 

 60 feet in height ; 

 the base is so 

 exceedingly ash- 

 like that speci- 

 mens were col- 

 lected as exhibit- 

 ing the fragmental 

 character of an 

 'ash.' Above the 

 base the section is involved and not easily interpreted, and higher 

 up are large included masses of black slate disposed generally 

 parallel to the base, which, on the hypothesis of the mass being 

 intrusive, represent the remnants of sedimentary pre-existing strata, 



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