382 Studies on the Palfeozoic Soils of North Wales 



Now on microscopical examination it is seen that the fine gravel 

 and, to a large extent, the coarse sand, consist of unaltered rock. In 

 one case, D 18, a sample of the parent rock was obtained and found 

 on analysis to have precisely the same composition (estimating SiOg, 

 AI2O3 and FcgOg) as the fine gravel of the derived soil. Had other 

 samples of parent rock been available this would doubtless have been 

 the case in all the samples, for the fine gravel is usually composed of 

 angular rock fragments. More experimental work is needed but 

 the analyses of the ten sets of soil fractions do suggest that for North 

 Wales at any rate, the more siliceous the parent rock the larger are 

 the particles of highest silica content; and, on the other hand, the 

 lower the content of silica in the parent rock, the finer are the particles 

 containing the highest proportions of silica. It is proposed to enquire 

 into this more closely, performing complete analyses of the fractions. 



Considering that the North Welsh Palaeozoic soils contain such a large 

 amount of undecomposed rock material even in the material of smaller 

 grades than the fine gravel, it would appear that they form a class 

 similar to that described by Ramann as Steinb()den, i.e. soils which 

 consist mainly of slightly decomposed rock fragments^. Ramann 

 further divides these soils into three sub-classes according to the size 

 of the rock particles. In North Wales, all gradations can be found 

 from masses of bare boulders to soils in which very little coarse material 

 is found. Ramann believes soils of this class to be the result of 

 mechanical weathering and it would appear that this is true to a large 

 extent for the North Welsh soils. It should be added that Ramann's 

 8teinb5den are soils from mountainous areas. 



It is worthy of notice that the clay of North Welsh soils shown in 

 the Table contain generally smaller percentages of silica and higher 

 percentages of alumina and ferric oxide than the most extreme types 

 quoted by Hall and Russell ^ for infertile soils. It should be stated 

 that, of the soils whose fractions were examined, all except D 18, D 33, 

 D 45 and C 18 were of soils of considerable fertility. 



4. The North Welsh soils are generally deficient in calcium car- 

 bonate. It is very rarely that one meets with this soil constituent 

 except in limestone soils. This poverty in calcium carbonate is readily 

 understood when it is considered that limestone scarcely occurs in the 

 rocks of North Wales of Silurian and earlier periods. A few outcrops of 

 limestone are found associated with the Pre-Cambrian rocks of Anglesey. 



1 Ramann, Bodenkunde, 1911, p. 543. Steinboden sind Bodenartcn, die sich iiber- 

 wiegend aus wenig zersetzten Gesteinsbruchstiicken zusammensetzen. 



2 This Journal, vol. iv, pp. 181-223. 



