148 ~ THE Rey. MAXWELL H. CLosE, 
Carboniferous Limestone Proper.—This has been separated 
into three divisions, Lower, Middle, and Upper. ‘The distinction 
between these, however, is principally lithological 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. In this district the Lower Lime- 
stone is generally a pale grey crystalline limestone, sometimes 
reoularly 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, interstratified 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 
Liffey and the foot of the Dublin hills the prevailing dip of the 
Limestone strata (neglecting slight contortions) seems to be every- 
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 8S. 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 
en the shore at Blackrock in the People’s Park, In a Limestone 

