Dec. 12, 1884.] 



♦ KNOWLEDGE ♦ 



483 



" the ISIenai Straits is nothing but a glacial groove on a 

 grand scale." The glaciers tore off the rough crags, 

 smoothed down the prominences into rounded hummocks, 

 and carried along with them all the debris, forming the 

 boulder-clay which is now visible at many points along the 

 coast, and which covers over the stratified rocks and renders 

 their examination difficult. In ordinary geological maps all 

 these surface deposits are supposed to be swept away, and the 

 various colours on the maps show the different beds of stra- 

 tified rock which are believed to lie beneath the drift ; but, 

 as a matter of fact, these glacial beds offer a great obstacle 

 to our study of the older underlying strata. It has at 

 last been resolved by the Government Survey to publish 

 a douhh set of geological maps ; the one (as in the present 

 maps) showing the regular stratified rocks only ; the other 

 giving the surface of the country as it actually exists, the 

 deposits of sand, mud, boulder-clay, &c., being indicated by 

 distinct colours — the stratified rocks only shown where 

 they form the actual s\irface upon which we walk. A few 

 such " Drift Maps " for jjarts of the eastern counties of 

 England have already lieen published. 



The manner in which the ice (which, as Faraday and 

 Tyndall have shown, acts, when under pressure, like a 

 plastic substance) accommodated itself to the irregularities 

 of the surface, flowing down one side of a valley and up 

 the other, is strikingly shown by a large block of green- 

 stone built into the playground wall of the school at 

 Criccieth. Deep and broad grooves — effected by stones 

 frozen into the superincumbent ice, and carried along with 

 it — run along one face of the block, and are continued on the 

 next face, passing round the corner of the stone with scarcely 

 a break. Dr. H. W. Crosskey has noted similar examples 

 in basalt blocks from the Rowley Hills near Dudley, and 

 he found a block in a Swiss moraine showing exactly the 

 same thing. Many of the stones in the boulder-clay form- 

 ing the low coast cliffs west of Criccieth and in Forth- ceiriad 

 show grooves and striations, and their surfaces are often 

 smoothed. The included stones are mostly of local origin, 

 but along the west coast, as between Bangor and Clynnog, 

 fragments of granite which can be referred to the Lake- 

 district, are not uncommon. 



After the retreat of the glaciers, the land appears to 

 have been depressed at least 2,000 feet. This is shown by 

 the patches of sand and gravel, containing shells, which 

 occur on the hill-side.'. At i\Ioel Tryfan, five miles south 

 of Carnarvon, there are slate quarries at a height of 1,150 

 feet, and from the gi-avels which here rest upon the eroded 

 surface of the slates Mr. Etheridge has identified fifty-five 

 species of shells of species such as now flourish in the seas 

 round Iceland and Greenland. This subsidence was fol- 

 lowed by an elevation, during which local glaciers again 

 fiUed the valleys, and more boulder-clay was formed 



Fig. 2. — Slate Quai-ry on Moel-Tryfan. 1. Cambrian Slates ; 

 2. Sand and gravel, with sea slielU; 3. Boulder clay (after 

 Kamsay). 



(Fig. 2). From that time down to the present day other 

 agents of denudation have" been at work upon the rocks of 

 Lleyn. The sea has hollowed out the softer strata into 



bays and inlets ; frost has done its wintry work, detaching 

 block after block to form the " screes " which lie at the foot 

 of the " scars ; " the rivers have made new valleys, remov- 

 ing a large part of the boulder-clay with which the ancient 

 valleys were filled up ; and the rain has aided all these 

 destructive agents in their task. By these means much of 

 the efiect of the levelling and smoothing-down done by the 

 great ice-sheet has been obliterated ; but although the 

 scenery of Lleyn is to-day full of the most charming 

 variety, yet the evidences of its bygone vicissitudes ai-e, to 

 the geological eye, written clearly upon its surface. 



Pre-historic Man in Lleyn. — The stone implements, 

 which elsewhere mark the first appearance of man upon 

 the surface of the earth, occur but scantily in Carnarvon- 

 shire. Mr. Darbishire found a roughly-chipped stone celt, 

 or axe-head, at Penmaenmawr, another, not far off, at 

 Dwygyfylchi, and a net-sinker (an oval stone with a groove 

 round it) at Nantlle. Near Aber there is a large stone 

 called Carreg-y-saelhan — stone of the Arrows; it has 

 numerous scorings upon it, from one quarter to half an-inch 

 in depth ; but, although it was doubtless used for sharpen- 

 ing tools or weapons of some kind, Mr. Evans thinks it 

 belongs to the Metallic Age. In cairns which he opened 

 near Bangor, Colonel Lane-Fox found numerous rough 

 flakes and splinters of stone, some of which showed signs 

 of rubbing and use on their edges. 



Of the Bronze Age — which succeeded the Stone Age— 

 we have a trace in the small bronze dagger-blade which 

 was found, together with a wooden bodkin, at Tomen-y- 

 mur, in an urn, also containing burnt bones. 



But the fortifications on the hill-tops, and the cromlechs, 

 are the most striking remains of early man which this 

 region affords to us. The camp on Trer Ceiri — a peak of 

 Yr Eifl — is on a very extensive scale. A double or treble 

 wall of great thickness and extent, and still many feet in 

 height, encloses a number of circular, hut-like stone dwell- 

 ings. Professor Ramsay calls it, " by far the most striking 

 hold of the kind I have seen in any part of Britain, with 

 its broad parapeted unmortared walls, its flanking defences, 

 and its numerous ruined houses, chiefly circular, enclosed 

 within its bounds." Almost every prominent steep hUl- 

 top, as Moel-y-gest, Carn Madryn, Cam Boduan, &c., bears 

 traces of similar camps, possibly erected by the ancient 

 Gaelic inhabitants during the troublous times in the fifth 

 and sixth centuries, which followed the departure of the 

 Romans. 



The cromlechs are, without doubt, the burying-places of 

 the chiefs of these early tribes. They are now seen as 

 broad stones, usually five or six feet square, supported by 

 three or four massive corner-stones, four or five feet in 

 height. Probably they were once covered completely with 

 a mound of earth, but this covering has been removed 

 by rain and frost, and by the eager hands of intruders in 

 search of gain, for the mounds, or tumuli, were formerly 

 considered to contain great treasures. There are two fine 

 cromlechs about a mile north of Criccieth. Two others 

 lie three miles north of Pwllheli, but one of these (the 

 northernmost) has only a single stone remaining (if it ever 

 had more, which is very doubtful). There is a fine crom- 

 lech near Clynnog, between the village and the sea-shore. 



The geologist who visits Lleyn will never regret the 

 time spent there. The eastern part — between Criccieth 

 and Portmadoc — is most interesting to the lover of fossils 

 — the palajontologist — while the student of rooks (the 

 petrologist) will find the extreme west — the tract between 

 Pwllheli and Bardsey Island — a new land, full of problems, 

 which, if he can work them out, will lead him into the 

 eart of the most-debated topics of the geological world, 

 ut for every one this corner of Wales offers lovely 



