392 



Scientific Proceedings, Royal Duhlin Society. 



combination of sea-salt, (jomminuted fragments of shells, and the porous 

 nature of the sand, which permits the removal of bicarbonates, results in a 

 reaction which is always alkaline, often marlsedly so up to near pH 9-0. To 

 this probably the high temperature reached by sand in the sunlight also 

 contributes, as the bicarbonate may be partly decomposed by this. 



It may be added that the Devonian Slate cliffs at Pentire are, in spite of 

 their neighbourhood to the sea, slightly acid, pH 6-6-7'0, whilst the i3illow 

 lava or spilite forming the extremity of Pentire Head yields a slightly acid 

 soil, pH 6'8. It is probably due to the wind-borne spray that the acidity is 

 not greater. 



It seems possible that within limits the determination of hydrogen ion 

 concentration given by the soil or by the rocks themselves may be of some 

 use in working out relationships of displaced strata where fossil evidence is 

 wanting or scanty. Thus, a slaty or sandy soil may be acid in certain 

 situations, but it is its limit on the alkaline side that may serve to 

 distinguish it. 



In this work use has been made of Ussher's (1907) memoir on the 

 Plymouth district. 



Table I. 



Geological formation. 



Nature of rock. 



Locality. 



Soil. 



Typical 



■pH 



values. 



Lower Devonimi. 

 Dartmouth Slates, . 

 Staddon Grits, 



»» J) 



Intrusive, 



Middle Devonian, . 

 ff ^> ■ 



Upper Devoiiiiin. 

 Volcanic and slates, 

 Upper Dev. slates, . 



Volcanic, 

 Plutonic, 



Slaty, 

 Sandstone, 

 Slaty, 

 Felsite, 



Slate, 

 Limestone, 



Schalstein 



slates. 

 Slaty, 



and 



Pillow lava (spilite' 

 Granite, 



Rame Hd. and in- 

 land. 



Staddon Heiglits 

 and Maker. 



Staddon Heights, 



Kingsand, 



Staddon, 

 Plymouth district, 



Compton, 

 Egg Buikland, 

 Pentire Hd., 

 Pentire Hd., 

 Dartmoor, 



Glenoullen, 

 Dublin. 



Co 



Light soil, dark 



brownish. 

 Sandy, deep red, 



Light soil, brown- 

 ish. 



Shallow blackish 

 soil, with plant 

 remains. 



Light, brownish 

 yellow soil. 



Somewhat sandy, 

 light brown to 

 black. 



Brownish soil, light 



texture. 

 Dark brown light 



soil. 



Shallow light soil, 



Disintegrating 



granite. 

 Purely peat, 



6-7-7'3 

 7-1-7-8 



5-4 

 5-4-6-4 



6'0-8-4 - 

 7-4-9-0 



7-4 

 5-8-7-0 

 6'6-7-0 



6-S 



5-2 



4-6 



