THE RIVER VALLEYS OF SOUTH-WEST IRELAND. 173 



The first of these propositions Mr Jukes subse- 

 quently gave up, and had to allow that the opinion of 

 more than one of his colleagues was probably right, 

 namely, that the carboniferous slate and Coomhola- 

 grits of S.W. Cork were the representatives of the 

 carboniferous limestone of the central plain, and that 

 the latter rock never existed in that country. This, 

 however, does not much affect the present subject, 

 as some of the other rocks are nearly as easily de- 

 nuded as limestone. Of the other propositions, none 

 seem to us to be proved. We shall begin with the 

 second and sixth taken together. 



In the river valleys of S.W. Cork we find the 

 geology concealed by alluvial deposits, the relations 

 of the rocks on one side of these flats to those on the 

 other being only conjectural, and on account of the 

 high dips of the strata, considerable faults might 

 exist without their being observed ; which seems all 

 the more probable, from the fact of rocks sometimes 

 coming down one side of a valley while there are none 

 on the other side. 1 Besides, all the valleys in the 

 country that extend northward and southward are in 



1 In the valley of the Boyne, where the viaduct crosses the river, in 

 the vicinity of the town of Drogheda, there is no surface appearance of 

 a fault further than the river valley ; yet when sinking the foundation 

 for the piers of the bridge, at 20 feet on the Meath side nearly horizontal 

 calp limestones were found, while for the Louth pier an excavation 

 over 90 feet deep was sunk without coming to any rock, there being 

 between the two places a great downthrow to the northward. 



