156 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [ Dec. 22, 
the hard and black basalt of the interior and the purple or yellowish 
argillaceous masses in which the basalt appears to be imbedded. 
Again, the boles often contain cavities filled with the ordinary zeo- 
lites of the amygdaloid basalts. Portlock* gives an analogous case of 
the production of ochre from an allied rock. ‘The greenstone in the 
Glenrandal river in Upper Cumber,” he says, “is so highly charged 
with iron as to disintegrate into extensive beds of a very rich ochre. 
The ochre is sometimes in the state of hydrate and yellow, and at 
other times red. The mode of alternation is :—felspathic mica-schist, 
or gneiss, compact below, but quite rotten and decomposed at the top ; 
ochre graduating into a decomposing greenstone. * * * * The green- 
stone also occurs within the ochre, and by its decomposition gradually 
merges into it. * * * In a branch stream to the west, the ochre is 
met with alternating with less altered greenstone, the thickness of 
the greenstone being 26 feet, and of the ochre 18 feet. And in the 
townland of Aughlish, in Banagher, it is upwards of 50 feet thick, 
several patches of greenstone within the mass being still solid, and 
merging into ochre.” 
Observations in the field and the following comparative analyses 
go far to prove that the bole and lithomarge are the resultants of 
aqueous action in combination with acidulated gases, which, dis- 
solving out certain mineral substances, has effected the decomposi- 
tion of the basalts, especially the more felspathic ones. 
Table of Analyses of Basalt, Inthomarge, and Bole. 
it. II. III, IV. y. 
Bas. Bas. Lith. Och. Bole. 
Gila 5, 1S en eon ewennecunlinwact 39°72 53°70 49-75 56:40 30°88 
IAIN AS, cae cance hereciots 14:32 2541 29:88 3°46 20°76 
Peroxide of iron .............., 27:87 8°95 6°61 24-14 26°16 
Tinie ae ae 4-15 4-55 0:43 0:90 2°60 
Magnesia ..............2... 00 ceee 4.00 eee Meal e  ponbas | || 2eccec 
Sulphuretofparon-nee- eee ess: > Bongos pucc0e = gancce 
Sod aire grace acscnc chases seaeeeree | oSaliiic! ah ayn each an My oie eche ste MMe eset 
Potash. -scsacetsec cease eesseseee OD GA WI oscene 6°35 NWSI). veasdes 
Waist Salad ee 430 448 as 19:60 
I. Basalt, Slieve Gallion (Dr. Apjohn). II. Basalt, Antrim 
(Prof. Hodges). III. Lithomarge, Germany. IV. Ochre of the 
Basalt, Drumrankin, near Ballymena (Dr. Apjohn). V. Bole, Ger- 
many. 
The chief differences in the chemical composition of bole, litho- 
marge, and basalt are the increased percentage of peroxide of iron 
and water, and the less quantity of alkalies in the boles and litho- 
marges as compared with the basalt. 
The alternation of basalts and boles indicates successive lava-flows 
of the more easily decomposed and the crystalline materials, the 
former having subsequently disintegrated into bole or lithomarge, 
while the latter has persisted tolerably well. In those instances 
where there is a passage from the hard rock below to the soft, and 
from the soft to the hard above, the basalts overlying and underlying 
* Geol. Survey, Derry, p. 173. 
