456 Henry H. Hoicorth — Geology of the Isle of Man. 
VIII. — Geology of the Isle of Man. 
By Henry H. Howorth, Esq. 
( Concluded from page 413.) 
I N my former note I adduced the reasons which make me confident 
tkat the conglomerates of the south of the Isle of Man, which 
have been hitherto classed as Devonian, are not Devonian, but are 
later than the Carboniferous Period. I will now tum to the problem 
of what they really are. It is a well-known fact tkat in the Isle of 
Man the Secondary and Tertiary rocks are wholly absent. This is 
the view of all those who have examined the island, and is in fact 
perfectly palpable. The series of older rocks terminates with the 
upper layers of the Carboniferous Limestone; above this tkere 
are nothing but deposits of Quaternary Age. The red con- 
glomerate to which I have referred contains no trace of any Second- 
ary or Tertiary fossils, nor is there the smallest ground for believing 
that it belongs to either of those series. Does it then belong to the 
Quaternary beds ? This conclusion is inevitable, and, as we shall 
see, is an exceedingly interesting one. 
The deposits of the Pleistocene age are developed in the Isle of 
Man on a very large scale, and the series may be there studied in 
detail, and especially the Boulder-clay formation. One of the 
peculiarities of the Boulder-clay in the Isle of Man is the large 
proportion of local or insular materials that have built it up. 
This has been noticed by Mr. Cumming ( op . cit. page 113). 
Here let me make a small digression. If, as is almost certain, 
the matrix in which the boulders are imbedded was formed out of 
the subjacent rocks, ground down and pulverized by moving ice, 
it is quite clear that what will be clay in one Situation, wliere the 
materials for making clay exist, will be an entirely different sub- 
stance elsewhere. That the same sheet of shore-ice, which in scrap- 
ing over the upturned edges of Silurian schists makes excellent clay, 
will, within a few yards of the same place, and perfectly contem- 
poraneously, be making a bed of a pasty texture out of the Mountain 
Limestone immediately adjoining, while if it was plougliing down 
the surface of Secondary and Tertiary rocks, the resulting product 
would again be different. I don’t know (and claim the privilege of 
a mere student in suggesting) but it may be that those who have 
mapped out the Quaternary Deposits of Europe have not sufficiently 
attended to this crucial fact, namely, that they have looked for Boulder- 
clay where no clay could possibly be found, and that they have placed 
on a different horizon some really contemporaneous bed made of dif- 
ferent materials. 
In the Isle of Man, at all events, we must take this fact into con- 
sideration, and we have our lesson very palpably laid down for us. 
Where the hasset edges of the schists are exposed, we find the ad- 
joining drift deposits to be almost pure clay. Where these beds 
change colour, so do the superincumbent clays. Where we near the 
horizontal beds of limestone deeply scored in various directions, we 
find more and more lime in the clay, which becomes a veritable tilth. 
