354 Studies on the Palceozolc Soils of North Wales 



PalcBozoic Silt Loam.. 



This is the best defined and the most widely spread soil type hitherto 

 encountered in North Wales. It covers practically the whole of 

 Denbighshire and occurs to a more limited extent in Central Anglesey 

 and parts of South Carnarvonshire. Outside of the district investigated 

 in the present paper it covers a considerable area. It extends southward 

 over a large part of Merionethshire and through South-west Shropshire 

 and Montgomeryshire into South and Central Wales, where it probably 

 attains a very large extent. The Palaeozoic silt loam is therefore one of 

 the most important soil types hitherto encountered. 



These soils are derived from the weathering, generally in situ, of the 

 sedimentary rocks of the Cambrian, Ordovician and Silurian formations. 

 The rocks in question form an enormous succession of shales, mudstones, 

 flags and grits. It is much to be regretted that petrologists have so 

 neglected the sedimentary rocks, particularly the older shales and 

 flagstones. Practically no literature is available on the petrology 

 of the North Welsh Palaeozoic sediments although the igneous rocks 

 have been exhaustively studied by Harker, Teall and others. Litho- 

 logically these rocks vary from extremely soft shales to hard flagstones 

 such as are found in the Cambrian area around Portmadoc. All the 

 rocks can however be cut with an ordinary knife. The slates of North 

 Wales are of course metamorphosed sediments, but a considerable 

 degree of metamorphosis has occurred in the rocks not usually thus 

 regarded, for many of them are sub-crystalline. 



Associated limestones are almost lacking in North Wales, although 

 eastward in Shropshire and Staffordshire large masses of limestone 

 occur in the Silurian formation. It is almost certain that the shore- 

 line at the time of deposition lay westward, in the direction of the 

 Irish Sea. 



In North Wales the Palaeozoic silt loam is fairly uniform in character, 

 the variations being due generally to water content and situation. 

 Typically, it is a rather stony medium loam of variable but generally 

 satisfactory depth. The colour varies from grey to brown in the soil ; 

 the subsoil is often yellow or Hght brown and contains high proportions 

 of stones and gravel from the underlying rock. Most of the soil up to 

 about 1000 feet is fairly well drained naturally but at higher elevations 

 the land is often wet. A large part of the central uplands of Denbigh- 

 shire consists of stretches of rather wet heather moor with accumulations 

 of peat in the depressions. 



