B. IT. Chandler — Unrecorded Erratics. 221 



Mr. J. V. Elsden, B.Sc, F.Gr.S., kindly examined a microscopic 

 section, and pronounced it to be "a typical enstatite-diabase, precisely 

 like parts of the St. David's Head and Cam Llidi masses. I should 

 say it certainly comes from there ". There is a little drift containing 

 igneous rocks in the immediate neighbourhood, capping the limestone 

 plateau, and increasing to 6 feet at Pen-y-holt, 3 miles to the west ; 

 and a Boulder-clay 8 miles to the north-west. 



By the roadside at Fliraston Cottage (near Flimston Coastguard's 

 Station) is a boulder roughly 3 ft. X 2 ft. X 2 ft. 3 in. high, weighing 

 about 15 cwt., and having a very much weathered, rugose surface. 

 Mr. H. H. Thomas, B.A., P.G.S., who kindly examined two slices of 

 this boulder, regards it as "a brecciated spherulitic albite trachyte or 

 rhyolite ". He adds : " Rhy elites occur at a great number of places in 

 Pembrokeshire, and all these rhy elites are not strikingly dissimilar 

 from each other, but of all those that I have examined the Flimston 

 Boulder seems to fit best with those of Boman's Castle, in the 

 character of its spherulites and groundmass. I should think that it 

 would be fairly safe to refer the boulder to that source." 



Another large boulder occurs at Holloway Farm, Penally (used as 

 a stQ,p to the wall of the farmyard), about 5 ft. X 1 ft. 6 in. X 1 ft. 

 high, weighing approximately 9 cwt. ; also a similar, but smaller, one 

 on the foreshore at Lydstep Caverns, about 3 ft. X 1 ft. 6 in. X 1 ft. 6 in. 

 and weighing about 7 cwt. Microscopic sections of each of these show 

 ophitic structure, and are said by Mr. J. Y. Elsden "to be in every 

 respect identical with the rhombic pyroxene rocks of St. David's Head, 

 and maybe described as enstatite-gabbro or norite". The Holloway 

 section, which is taken from the partially weathered crust, is not 

 nearly so fresh as the one from the Lydstep shore ; owing to the 

 action of the sea on the latter the unaltered core is exposed, otherwise 

 the two rocks are identical. 



Another boulder, which occurs in the quarry on Lydstep Head, 

 is a grit composed of angular quartz grains with some plagioclase 

 felspar and mica, but is not distinctive enough to trace to its source ; 

 in size it measures roughly 3x3x2 feet, and would weigh about 

 13 cwt. 



These three latter boulders (Lydstep Caverns, Lydstep Quarry, and 

 Holloway Farm) are in an area almost devoid of drift on the cliff top, 

 although igneous pebbles are abundant on the shore. 



A glance at the map will show that the three boulders from 

 St. David's Head have come over 30 miles from the north-west, and 

 are separated from their parent rocks by St. Bride's Bay and Milford 

 Haven, and by a considerable mass of fairly high ground (up to 

 250 feet o.d.). 



The boulder from Roman's Castle is nearly 10 miles due south of 

 its probable source, from which it is separated by Milford Haven and 

 some high ground. Thus it is far from obvious by what route these 

 erratics reached their present positions, although it might be by the 

 Irish Sea Ice-sheet driving a stream from St. Davids eastwards over 

 sea and land to deposit its boulders south-east of their sources,' 



1 F. W. Ilarmer, Quart. Jouru. Geol. Soc, 1907, vol. Ixiii, p. 474. 



