269 
Geological Relations of the East rf Ireland \ 
porous spongiform mass conf^nonly remains, which in the estima- 
tion of some mineralogists might pass for the scoriae of lava, or 
even for pumice-stone. The rock may be traced in different 
stages of decomposition, from the firm solid compact state to the 
most porous ; the' former always exhibiting some degree of effer- 
vescence with acids ; the latter none whatever, when the pores are 
completely empty. 
The base of the trap conglomerate is an intimate mixture of 
greenstone^md carbonate of lime ; in which are imbedded angular 
fragments, sometimes of considerable size, of limestone, greenstone, 
and lydian stone. The compound shews in general on the fresh frac- 
ture a light bluish grey base, but this being extremely subject to 
decomposition, and disintegrating, there remains a coherent mass 
of unchanged fragments with numerous cavities and interstices j 
presenting a great variety of colours, dirty brown, yellow, and even 
brick red. 
The soil of this hill is remarkable for its fertility, yielding unin- 
terruptedly the most abundant green and white crops, without any 
manure whatever. 
Between Croghan hill and Philipstown, about one quarter of a 
mile from the latter place, massy strata of greenstone appear in the 
townland of Castle Bar nock, dipping 45° toward the west. The 
rock is compact, fine grained, and of a blackish green colour, con- 
taining disseminated particles of hornblende and calcareous spar. 
About half a mile to the west from the place where it occurs, are 
quarries of limestone, which contain subordinate layers of lydian 
stone, and thin beds of slate clay, dipping 16° toward the east. 
And in the limestone quarry at Philipstown to the south, a similar 
arrangement is obseryable, the beds dipping toward the east, but at 
