CHAP. XIX 
ERUPTIONS IN CANTYRE 
313 
neck, except by the rude bedding of the former which pas.s down into the 
well-bedded sandstones. 
The agglomerate is a thoroughly volcanic rock. The materials consist 
chiehy of angular blocks of a pale purplish or lilac highly porphyritic mica- 
porphyrite, with large white felspars and hexagonal tables of black mica. 
These blocks might sometimes be mistaken for slags from their cavernous, 
weathered surfaces, but this rough aspect is found on examination to be 
due to the decay of their felspars. 
Fig. 83. — Section of volcanic series on beach, Southend, Campbeltown. 
a, Fine reddish and purplish highly felspathic sandstones, largely composed of poridiyry-debris and passing up into 
coarse breccias ; h, volcanic breccias, coarse and only rudely stratilied, formed of blocks of porphyry, sand- 
stone fine tnff and ainlesite, together with water-worn quartzite jMibhlGS derivcfl from some conglomerate ; 
c, coarse unstratilied agglomerate forming a neck. 
Perhaps the most singular feature among the contents of this neck is 
the number of well-rounded and smoothed pebbles and boulders of quartzite. 
These are dispersed at random through the mass, and are often placed 
oil end. There can be no doubt that they are water-worn stones, hut the 
contrast of their smooth surfaces and rounded forms wdtli the rough angular 
blocks of igneous material is so striking as to lead at once to the conclusion 
that they cannot have acquired their water-w'orn character in the deposit 
where they now lie. Their positions and their occurrence wdtli ejected 
volcanic blocks suggest that they too were discharged by volcanic explo- 
sions. They so exactly resemble the quartzite boulders and pebbles in 
the neighbouring Old Pied Conglomerates that there can he little hesitation 
ill regarding them as derived from these conglomerates. They seem to me 
to have come from a lower part of the Old Picd Sandstone, wdiieh was 
shattered by volcanic energy either before the conglomerates were firmly 
consolidated or afterwards by such violent explosions as served to separate 
the pebbles from the matrix of the rock. 
There occur also in the agglomerate blocks of fine tnff and ashy sandstone 
sometimes four feet long, and often stuck on end, showing that the deposits 
of earlier eruptions were broken up during the drilling ot tliis little vent. 
A few hundred yards further east a larger neck rises on the beach, 
immediately to the south of the old Celtic chapel of St. Colnmha. It con- 
sists also of exceedingly coarse agglomerate, with andesite blocks three and 
four yards in diameter. It is about 125 yards lu’oad from east to west, 
on wliich sides it is seen to be flanked by coarse volcanic breccias and 
conglomerates, resembling in composition the materials of the neck, but 
showing an increasingly definite stratification as they are traced eastward 
in the ascending succession of deposits. Following the section in still 
the same easterly direction along the coast, we find that hands of fine 
felspathic sandstone, marking probably intervals of quiescence, are again 
