148 The Rev. Maxwell H. Close, 



Carboniferous Limestone Proper. — This has been separated 

 into three divisions, Lower, Middle, and Upper. The distinction 

 between these, however, is principally lithologieal and local in 

 character ; it cannot be generally carried out. The Middle division 

 seems to be the least constant, and about Dublin the Middle and 

 Upper are not distinguishable. Tn this district the Lower Lime- 

 stone is generally a pale grey crystalline limestone, sometimes 

 regularly bedded, sometimes in amorphous masses. The neigh- 

 bourhood of Dublin, for a radius of several miles, is on the Middle 

 and Upper Limestone which here consist generally of dark, 

 earthy limestone, called calp, interstratifled with dark grey shales, 

 and with frequent layers or irregular nodules of chert. This is 

 quarried for building stone and road metal. Occasionally beds of 

 good pale limestone, fit for burning occur therein ; these some- 

 times abound in fossils. 



The lower division of the Limestone lies directly on the Cam- 

 brian rocks at Howth, and its upper division, which has over- 

 lapped its own inferior parts, extends on to the Silurian rocks 

 near Skerries, and on to the Silurian rocks and granite at four 

 miles southward of Dublin. 



In the last mentioned vicinity the following remarkable cir- 

 cumstance is to be observed. Over all the district between the 

 LirTey and the foot of the Dublin hills the prevailing dip of the 

 Limestone strata (neglecting slight contortions) seems to be ever} r - 

 where southwards, or towards the emerging Silurians and the 

 granite. This may be partly explained either by undulations of 

 the beds whose opposite dips happen to be concealed, or by a 

 series of faults running nearly E. and W., which repeat the beds ; 

 otherwise it would be necessary to attribute to the black, earthy 

 limestone a thickness greater than the known thickness of the 

 group anywhere else. A similar peculiarity of dip may be ob- 

 served near the northern extremity of the map. The Upper 

 Limestone beds on the shore S. of Skerries and also two miles 

 inland dip northwards towards the Lower Silurian rocks on which 

 they rest. 



The actual contact of the Limestone and Cambrian is visible 

 on the W. shore of the Howth peninsula about 200 yards N. of 

 Bottle Quay. The contact of the Limestone and granite is nowhere 

 exposed ; the two are visible about a stone's-throw from each other 

 ©n the shore at Blackrock in the People's Park, In a Limestone 



