G. VV. Robinson 365 



aeid is also present in fairly high proportion. Calcium carbonate, 

 except in one or two samples, was always lacking. 



In order to determine whether the soils formed from Ordovician 

 material differed in any marked respect in composition from the main 

 type the results of 15 Ordovician soils were averaged. The figures, 

 however, except in the case of the fine gravel which was 2 % lower for 

 the Ordovician soils, did not differ by more than 1 % from the average 

 of the 49 samples of the series. Potash for the Ordovician soils was 

 •72 % as against -80 % and phosphoric oxide was -20 % as against 

 •185%. It seems evident therefore that there is no reason for 

 separating the Ordovician soils from the other soils of the series. 

 • A comparison with the Palaeozoic silt loams of Shropshire is instruc- 

 tive. In that county the soils of Ordovician and Lower Silurian 

 (Wenlock) age are considerably heavier than the Palaeozoic silt loams 

 of North Wales and many of them are properly described as clay soils. 

 The Upper Silurian (Ludlow) soils of Shropshire agree with the Palaeozoic 

 silt loams of North Wales in containing comparatively little clay, but the 

 dominant fraction is the silt instead of the fine silt. The rocks in the 

 two areas appear similar but the Shropshire strata were certainly 

 deposited in deeper water. Probably the original clay of the North 

 Welsh rocks has been altered by metamorphosis whereas the clay of 

 the Shropshire rocks may have survived from primitive times. The 

 matter is of considerable interest and is worth investigation. It should 

 be added that the Ordovician and Silurian soils of Shropshire are also 

 rich in potash but do not show such high figures for phosphoric oxide. 

 A large number of the Shropshire soils contain calcium carbonate. 



Carnarvonshire Stony Loams. 



These soils can scarcely be called a type. They form rather a series 

 of soils, and occur in the parts of Carnarvonshire between the mountains, 

 the northern coast and the line AB shown on the orographical map. In 

 texture they are gravelly or stony medium loams sometimes varying a 

 little on the light side and sometimes on the heavy side, but never 

 becoming sands or clays. As a rule stones and boulders become more 

 abundant as the mountains are approached. Geologically they consist 

 of material scraped down from the mountain area by local glacial action. 

 Generally the material is very much mixed but in certain places, a 

 particular variety of rock material is seen to be dominant in the soil and 

 can be referred to adjacent rocks in the mountain area. For example, 

 in the vallev immediatelv west of the summit of Snowdon, the stones 



