410 Henry H. Howorth — Geology of the Isle of Man. 
(Fig. 1, No. X.), sparlding like tke scales of a fisli, also excited mucli 
curiosity among tke natives. 
Tke siliceous ironstone is very difficult to fase in crucikle experi- 
ments witk tke usual proportion of limestone fluxes, even in tke 
intense keat of a puddling furnace ; kut I found tke klue Lias Clay 
an excellent flux, dedueting of course tke iron it contains (akout 
four per cent.) from tke result. Fossils were very scarce, and 
only tke usual Inferior Oolite specimens, witk a few small pkospkatic 
nodules being occasionally met witk of about an inck in lengtk by 
kalf an inck in diameter, in tke Nortkampton Ironstone bed. 
Several chalybeate springs find tkeir way into tke valley, and form 
tkin patckes of re-deposited iron ore. Tke dead leaves and twigs at 
tke bottom of ditckes being sometimes covered witk crystalline 
featkers of peroxide of iron.. as buskes and treea are occasionally 
decorated witk koar frost in winter. 
IV. — Geology of the Isle of Man. 
By Hexry H. Howorth, Esq. 
I N a recent visit to tke Isle of Man, I spent tkree long days in 
examining tke deposits of tke very interesting district in tke 
soutk of tke island, and I wisk to draw tke attention of your readers 
to some facts wkick are, I tkink, important. Not being an ex- 
perienced geologist, I kope I skall do so witk becoming modesty, 
and I should feel very gratified if some more practised geologist 
would verify my Statements, wkick are, kowever, not raskly made, 
as I kave sifted tke question witk care and patience. 
Mr. Cumming kas written tke most elaborate account of tke 
geology of tke Isle of Man, and kis work on tke island is an admir- 
able specimen of wkat suck a work ougkt to be. He is tke autkority 
for tke opinion now generally received, tkat tke Mountain Lime- 
stone wkick occurs under very interesting circumstances in tke bays 
of Derbykaven, Castletown, and Poolvask, is separated from tke 
underlying sckists by deposits of the Devonian or Old Bed Sand- 
stone period. Tkis conclusion, if true, would be very interesting in 
view of tke recent discussions as to tke relations of tke Old Red 
Sandstone to tke Carboniferous formation, since it is admitted by Mr. 
Cumming tkat the fossil s contained in tkese red rocks are identical 
witk tkose contained in the limestone. 
I believe the view of Mr. Cumming on tkis subject to be entirely 
erroneous, and tkat tke red rocks in question do not belong to tke 
Old Red formation, nor are they older tkan tke limestone, but tkat 
tkey in fact overlie that formation. There are four ways in wkick 
the age of tke deposit may be tested, and tke result in every case is 
conclusive tkat it is not Devonian. 
First, tke palmontological evidence. Into tkis I skall not enter. 
Mr. Cumming admits tkat tke fossils found in tke red deposit are 
the same as tkose found in tke limestone, and tkis fact is assuredly 
ä priori almost conclusive tkat the red rocks are not Devonian. 
Secondly, tke petrological evidence. Tke rocks in question consist 
