360 



D. MACKINTOSH ON HIGH-LEVEL MARINE DRIFTS. 



boulders. The summit of the ridge varies from about 1450 feet to 

 about 1500 feet. The well-rounded gravel-and-sand commences 

 about 1100 feet (west of Braich), and extends in a westerly direction 

 up to about 1350 feet. The hillocks (west of Braich), in one of 

 which I found numerous shell-fragments in a gravel-pit, range in 

 height from about 1100 feet to about 1250 feet. Above Mountain 

 Lodge (S. of Frondeg) there is a gravel-pit in a knoll about 1200 

 feet above the sea, and one further west (in which I found shell- 

 fragments) about 1230 feet. But the plateau, near the south edge of 

 which these pits are situated, consists of rounded gravel-and-sand, 

 which, in a westerly direction, rises to at least 1350 feet above the 

 level of the sea*. In the gravel-pits and in the neighbourhood 

 where sections are exposed in brook-channels, the stones, especially 

 in the Frondeg district, are very much rounded, more so, in fact, 

 than on the shores of the Irish Sea, where many of the stones (being 

 derived from drift-deposits) have undergone a double process of 

 rounding. This is the case especially with the Eskdale-granite 

 pebbles, which, in the Frondeg gravel-pit, are almost as numerous 

 as the local pebbles of Carboniferous grit or sandstone. In addition 

 to these, there are chalk-flints, pebbles of Lake-district felstone 

 and felspathic breccia, and local pebbles or fragments of Carboni- 

 ferous limestone,with much decomposing coal and many coal-measure 

 fossils, which can be best accounted for by supposing them to 

 have been locally worked up from strata now concealed under the 

 drift-deposits. In the Mountain-Lodge gravel-pits there are many 

 Carboniferous-limestone fossils, and much granite. 



2. Shell-fragments. —In the Frondeg gravel-pit shell-fragments 

 are very numerous, but I could find no whole specimens. This can 

 readily be explained by supposing that the excessive attrition to 

 which the extra-rounded pebbles were subjected must have extended 

 to the shells which were thrown up on the sea-beach. Among the 

 fragments I collected from the Frondeg gravel-pit, and partly from 

 one of the Mountain-Lodge gravel-pits, Dr. Gwyn Jeffreys has 

 identified the following species : — 



Cardium echinatum, Linne. Tellina balthica, L. 



C. edule, L. Mactra solida, L. 



Cyprina islandica, L. Mya truncata, L. 



Astarte borealis, Chemnitz. Fusus antiquus, L. 



3. Position of Boulders. — So far as can be seen in the gravel- 

 pits and brook-sections, the large angular boulders are chiefly to be 

 found in the clay, which extends under peat, from the west border 

 of the gravel-hillock zone up to near or (in some places) quite to the 

 summit of the mountain-range. They are likewise found, some- 

 times thickly strewn, on the surface of the clay, and to a less 

 extent on the surface of large mounds, which partly, at least, con- 

 sist of rounded gravel. They may also be seen scattered over the 

 lower country as far east at least as the railway. In the Frondeg 



* I have to thank the Director of the Ordnance Survey, Southampton, for 

 some of the above heights. 



