ON THE ERRATIC BLOCKS. OF ENGLAND, WALES, AND IRELAND. 323 
and two miles south of Rhayader the rocks of Carrig Gwinion present 
themselves as the source from which they all may have been derived. 
The specimens were very small—the largest being about one foot cube— 
and in no respect equal the remarkable assemblage of big blocks, previously 
described, on the long and high ridge forming the watershed of the Clun 
and Teme. ‘These fragments of grit, however, occur at considerable 
heights as well as in the valley bottoms—being found on the top of 
Beguildy Beacon, more than 1,700 feet above the sea. One block of 
Rhayader grit has been found north of the Clun river, but asa rule the 
lun river forms a northern boundary to this flow in a peculiarly sharp 
and striking way. A remarkable mixture of boulders occurs. Amongst 
the western boulders on the Clun Hills are (although few in number) 
quartzites from the Stiper Stones district fifteen miles north, and about 
Leebotwood, north of the Longmynd, are granites from Scotland or the 
Lake district. The flow of quartzites has overlapped and invaded the 
ground covered by the Plynlimmon stream, and the granites while doing 
the same with this local dispersion, have crossed the eastern stream of 
Arenig boulders. ; 
Professor Bonney writes that he is now satisfied, in consequence of 
information supplied to him by Professor Haghes, that the picrite boulders 
noticed by him in the Report for 1883 as occurring near the west coast of 
Anglesey, are derived from masses of rock which occur in situ to the 
north-east, especially from one near Caemawr. He has also received 
from Dr. H. Hicks specimens of a boulder of very characteristic horn- 
_ blende picrite, which the latter found lying on ‘ Dimetian’ rock, on the 
east side of Porthlisky harbour, near St. David’s. Its longer axis 
_ measured about a yard: in transverse section it was rather triangular, 
the shorter sides measuring twenty-two inches and sixteen inches respec- 
tively. No rock of the kind is known to occur in situ anywhere in the 
district. This is more fully described, and the origin of the Anglesey 
boulders discussed in a paper by Professor Bonney which has appeared 
in the ‘ Quarterly Journal of the Geological Society’ (vol. xli. p. 511). 
Mr. R. T. Andrews of Hertford has forwarded the Committee a cata- 
logue of blocks from that neighbourhood, showing that the materials 
generally spread over the north of Herts extend south to the Hertford 
district. These may be divided into three main groups. (1) Hertford- 
shire ‘ Pudding-stone’; (2) Compact sandstones; (3) Grits and coarse 
sandstones. The Hertfordshire ‘Pudding-stone’ is of course locally 
derived. The fine compact sandstones, with coarser sandstones and 
grits, are of the kind so common in the boulders of Hertfordshire and 
the adjacent counties, which have been fully described in the Report 
of the Committee for 1881. Mr. Fordham remarks upon this catalogue, 
that the derivation of the rocks cannot be stated with exactness, since there 
is little about the materials, as found in moderate sized fragments, to 
identify them with particular beds; but their characteristics generally 
show that in all probability some of them have been derived from the 
secondary rocks of the Midlands, while others have come from the millstone 
grits and other older rocks further north. The absence of igneous rocks 
in this catalogue will be noted. As igneous rocks are rare in the north 
of Hertfordshire, their apparent absence in the centre of the county shows 
that there has been a gradual diminution of igneous material towards the 
south, while at length in the centre of Hertfordshire they are certainly 
absent. 
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