Geological Relations of the East of Ireland. 195 
ing westward, we meet with a repetition of the same inflections 
that we noticed in the inlet to the eastward. First the erect, and 
then the inverted trough, accompanied also with an horizontal 
section visible at low water, shewing the continuity and con- 
vergence of the several layers one within another. I apprehend 
that similar concretions are also more or less distributed through the 
body of the hill ; as in the upper parts I have occasionally remarked 
flexures and variations in the line of dip, which do not seem to admit 
so readily of explanation on any other principle. 
On the western side of this inlet, the stratified rocks have resum- 
ed their south-western dip, at an angle of 82°, ranging 30° west of 
north and east of south. The western point itself is composed of 
massy quartz rock : and along this coast the promontories are com- 
monly of a quartzose nature, the sea having made its inroads and 
formed inlets mostly in those parts, where the rocks were of a more 
perishable composition. 
In the great quarries opened on quartz rock in the northern face 
of the Headland, for the construction of the piers and new harbour 
at Howth, I have occasionally remarked disseminated small portions 
of iron pyrites, copper pyrites, arsenical pyrites, and galena. In the 
quartzy clay slate, near the Great Light-House, I met with fibrous 
brown haematite ; and grey ore of manganese, brown ironstone, 
and earthy black cobalt ore, have been found on the south-western 
side of Howth. The discovery of the last mentioned substance is 
due to Dr. Stokes, Professor of Natural History in the University of 
Dublin. 
This diffusion of metallic substances through the mass of rocks, is 
a phenomenon much more general than is commonly supposed, al- 
though the particles are, from their minuteness, frequently imper- 
ceptible to the eye ; and it may serve to explain why quartz rock on 
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