536 Belt— On the " Lingula Flags^' ■ 



the surface, and thus more exposed to atmospheric influences. I ex- 

 amined as closely as possible the mussel -beds in the sand which caps 

 the Boulder-clay that appears on the coast higher up Conway Bay, 

 thinking they might perhaps turn out to be artificial accumulations ; 

 but I could discover no admixture of bones, or even of other shells 

 with them, with the exception of one or two specimens of Patella 

 and Littorina. These mussel-shell beds occur in the loose sand, with 

 no rock for their attachment, and are about 20 feet above the beach 

 in some places. I could find nothing in the pocket of Mytilus near 

 the great Midden save those shells, and they mostly had their valves 

 in approximation and undisturbed ; they are apj)arently unconnected 

 with the Midden. A general, though somewhat hasty search round 

 the greater part of the Orme failed to reveal any further traces of 

 Middens, although remains of raised beaches here and there, con- 

 taining a few shells, such as Patella, Littorina, etc., may be seen in 

 many places, and at very considerable heights above the present sea- 

 level. Some fissures also in the Limestone rocks can be traced in the 

 face of some of the quarries, which have been filled up with rolled 

 pebbles ; these are now cemented into a firm conglomerate by the 

 infiltration of carbonate of lime. I could find no shells or other 

 organic remains in the contents of these fissures, though Patella and 

 Littorma are to be found in the talus close by. 



[Note. —All the bones sent me by the Eev. J. M. Mello, from the Kitchen Midden 

 in the Great Orme's Head, were very much broken (old fractures) ; but I was enabled 

 to identify Bos longifrons; jaws, etc., of a small-horned sheep; Leg-bones of Canis 

 lupus, or Oanis familiaris ; tooth and vertebrae of pig ; and fragments of bones of 

 bird.— H.W.] 



IV. — On the " Lingula Flags," or " Festiniog Group " 



OF THE DOLGELLY DISTRICT. 



By Thomas Belt, F.G.S. 



[PART II.] 



THE accompanying section shows the succession of beds from the 

 Harlech grits, near the sixth milestone on the road from Dolgelly 

 to Trawsfynydd, across their strike in a south-easterly direction, to 

 the lower ash-bed of the Arenig group at the farm of Blaenau, five 

 miles north-east from Dolgelly. In this section all the beds occur 

 in regular sequence, although they are invaded by many intrusive 

 masses and dykes of diabase;^ only the larger of which are shown in 

 my section, as it would be impossible, on so small a scale to depict 

 the innumerable protrusions of this rock that occur in the district. 

 The section crosses, at Moel-Cors-y-garnedd, the southern flank of 

 the mountain Ehobell-fawr, which is the largest mass of diabase 

 in Wales. All along the eastern side of Ehobell-fawr the strata 

 are completely inverted, as shown in diagram, so that the Festiniog 

 beds (5 and 6) lie above the more recent Dolgelly beds (7 and 8)^ 

 from underneath which the Tremadoc beds (9) come up, overlying the 

 beds of slates and ashes belonging to the Arenig Group (10 and 11). 



* I follow Mr. David Forbes in calling these rocks diabase ; they are the " Green- 

 stones" of the Geological Survey. 



