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XL— ON THE THICKNESSES OF THE lEISH BEDDED 

 ROCKS, BY G. H, KIN AH AN, President Royal Geological 

 Society, Ireland, Plates 7 and 8. 



[Read, November 15th, 1880.] 



In these diagrams, which I now exhibit (vide Plates 7 and 8), the 

 thicknesses are probably less than they would be represented by 

 most geologists ; they have been, however, calculated with great 

 care, and in all cases where there was possibly a repetition of 

 beds by faults allowance has been made for this, and in those 

 groups which are of variable thicknesses only the mean thick- 

 nesses are given. The bedded eruptive rocks which occur at 

 particular zones are included in the thicknesses. 



In the right hand margin of the diagram full particulars are 

 given as to the localities where the different strata occur and 

 when they are best represented — and the zones in which re- 

 markable fossils, coals, eruptive rocks, &c., are found. In the 

 left hand margins the thicknesses of the strata are shown. 



[Note in Press.] — The sections of the Silurian rocks in N. E. Mayo 

 to the north-westward of Ballagliaderreen, and in Tyrone to the east- 

 ward of Sixmilecross are very similar ; having below and above, red 

 rocks of the " I)ingle beds " type, with between them green rocks 

 containing subordinate shales and impure limestones. These calcareous 

 rocks of the Co. Mayo have in them marine fossils, but as yet it has not 

 been positively proved that they occur in the similar rocks of the 

 Co. Tyrone. 



N.B. — Owing to an error, the scale on Plate Vll. is given as 25,000 

 feet to one inch, it should be 2,500 feet to one inch. 



