G. W. Robinson 341 



These figures are only approximate, but will indicate the general 

 wetness of the North Welsh climate. Comparatively httle cultivated 

 land is found under annual rainfall greater than 50 inches. 



Temperature records are somewhat scanty, but the general facts are 

 fairly clear. The mean winter temperature varies from 39° F. to 42° F. 

 and increases from East to West so that Anglesey and West Carnarvon- 

 shire are as warm in January as Devonshire. The elevated districts of, 

 the interior are naturally somewhat colder than the coastal districts. 

 The average summer temperature is somewhat less than the average 

 summer temperature of central and southern England. 



High winds are prevalent along the sea coasts during the months 

 from October to April. 



To sum up. North Wales may be described as an area with high 

 rainfall, cool summers and generally mild winters. 



Geology. 



Two main facts must be noticed in order to understand the geo- 

 logical structure of North Wales. (1) The rocks are mainly Palaeozoic 

 except in the Eastern portion where Triassic deposits occur under the 

 drift, and (2) the whole of the area has been glaciated. 



The Palaeozoic rocks which underlie most of the area and whose 

 resultant soils form the subject of this paper fall into three main groups. 



A. The Pre-Cambrian metamorphic rocks of Anglesey. These 

 rocks which cover three-quarters of the area of Anglesey consist of a 

 series of schists and gneisses of variable composition. Rocks believed 

 to be of the same age occur in the extreme west of Carnarvonshire but 

 are generally obscured by drift. The Pre-Cambrian rocks rarely rise 

 to more than 400 feet and in no case more than 750 feet. 



B. The main part of Carnarvonshire consists of Ordovician strata. 

 With these are associated enormous masses of igneous and volcanic 

 rocks which form the core of the mountain area. 



C. Ordovician and Silurian shales and flagstones occur without 

 associated igneous rocks in Denbighshire and Flintshire, and form the 

 greater part of the area of the former county. They are generally free 

 from external drift. 



Cambrian shales and slates occur in a broad strip parallel to the 

 Menai Straits and in a few other places but do not give rise to any 

 extensive area of soil. The other Pala?ozoic rocks of North Wales, 

 including Old Red Sandstone and Carboniferous rocks, are of secondary 

 importance from the point of view of the soil investigator. 



Joum. of Agric. Sci. vni 23 



