Geological Relations of the East of Ireland \ 225 
The diffusion of calcareous matter is so general through the 
greywacke, greenstone, and slaty rocks of this coast, that few 
varieties can be found which do not effervesce with acids, even 
when nothing calcareous is visible to the eye. 
Rocks of this description, greywacke slate and clay slate with thin 
layers of limestone, and fine grained greywacke with massy beds of 
limestone and limestone conglomerate, now occupy the coast for a 
considerable distance to the southward in undulated stratification; 
the slaty rocks forming the predominant superincumbent mass, while 
the general range is nearly east and west throughout. 
Compact greenstone now appears, near the southern martello 
tower; some of which is porphyritic, and traversed by numerous 
contemporaneous veins of quartz. It is succeeded by fine grained 
greenstone slate passing into clay slate, which contains fragments 
and spots of clay slate, quartz, and calcareous spar. This rock rests 
upon the compact greenstone, ranging east and west, and dipping 
45° south. More south we meet with compact greenstone again, 
resting upon the greenstone slate. It is porphyritic, and about 100 
yards from the martello tower it consists entirely of greenstone 
porphyry, in which the felspar crystals are closely crowded together. 
But immediately under the tower we have greenstone slate again, 
similar to that before described. It seems nearly allied to the coarse 
.clay slate or greenstone conglomerate, into which it probably passes; 
is of a mottled aspect, greenish or purplish in colour, and of this 
description is the whole rock south-east of the martello tower to 
the sea. 
To the south of the martello tower, the beach is lined with sand 
Hillocks, which extend to the inlet from the sea, that leads up to 
Malahide. 
§ 123. In the higher grounds of Portrane, as in the Park and 
Vox.. V. 2 * 
