82 DR T. J. JEHU ON 
The most striking fact in connection with the erratics is that so many of them can 
be traced to the south-west of Scotland. The Ailsa Craig paisanite has been obtained 
in the boulder-clay, and is frequently met with on some of the beaches, especially at 
Abermawr. The granites, diorites, and porphyrites of the Galloway country are also 
well represented, boulders being found which represent the three principal massifs, 
namely, (1) Dalbeattie and Criffel, (2) Cairns Muir of Fleet and New Galloway, and 
(3) Loch Doon and Loch Dee, and in addition some from smaller exposures, such as 
that of the Mull of Galloway. 
The other region from which the boulders have travelled is the north-east of 
Ireland, and its rocks are represented in Pembrokeshire by reddish granophyres, quartz- 
porphyries, and micro-granites. 
A few boulders are found also which have almost certainly come ultimately from 
the Western Isles of Scotland. 
It is a noticeable feature that the Lake District rocks are but poorly represented, 
and the same is apparently true of those of North Wales. 
Many of the boulders and pebbles, such as those of Carboniferous Limestone and the 
chalk-flints, may have been torn up from the bed of the Ivish Sea. 
VI. GENERAL CONCLUSIONS. 
The facts adduced in this paper prove conclusively that northern Pembroke- 
shire has been the theatre of glacial action to an extent greater than had previously 
been supposed. Glacial deposits cover the ground in that part much in the same 
way as they do further north, and present very similar characteristics. Here also we 
meet with a tripartite division of the deposits, namely, a Lower Boulder-Clay, Inter- 
mediate Sands and Gravels, and an Upper Boulder-Clay and Rubble-Drift, reminding 
us of the tripartite division found at so many places further north on both the east and 
west sides of England, and in North Wales. But in the present state of our knowledge 
it is very difficult to correlate the deposits found in one area with those found in 
another area; and it is not safe to assume that the Sands and Gravels always represent 
any definite horizon in the glacial series. 
Of the deposits which have been described it is the Lower Boulder-Clay which has 
the widest extension ; it covers much of the lower grounds inland, and is often hidden 
under the other accumulations. It follows the slope of the ground, and a little below 
Pen Creigiau Cemmaes it attains an elevation of nearly 600 feet above sea-level. The 
series of sands and gravels is a very variable one. Often they taper or die away 
suddenly into a stony or loamy drift, and at places are absent altogether. They attain 
their greatest elevation near the east end of the area at Pen Creigiau, where the sands 
reach a level of over 640 feet, and are followed immediately below by coarse shingly 
gravel. The Upper Boulder-Clay, where the sands and gravels are absent, is some- 
times seen to rest immediately upon and coalesce with the Lower Boulder-Clay, so that. 
