122 The Irish Naturalist, May, 



The great difference that formerly existed iii the views of 

 geologists as to the general mode of origin of the drifts in the 

 British Isles has, however, practically disappeared. The 

 discovery of the nature of eskers — or, rather, the belated re- 

 cognition of what Hoist, Hummel, and Goodchild had written 

 on the subject — was the last blow to those who regarded widely 

 spread drifts and glacial striae as due to the stranding of ice- 

 bergs in a sea. The present Memoir includes a photograph 

 (p. 51) of the recently revealed water- worn surface of Carboni- 

 ferous limestone underlying the Green Hills esker near 

 Crumlin. The other photographs of glacial phenomena, also 

 by Mr. R. Welch, give additional distinction to the Memoir. 



Pp. 129-147 are concerned with Economic Geologj^ and Mr. 

 J. R. Kilroe gives a valuable description of the relations of 

 the drift to surface-soils. One of the most noteworthy points 

 brought forward is the partial decalcification of the soils (p. 

 142) to a depth of two feet or more, wherever water is moving 

 through them. Should this water, however, remain at vsuch a 

 depth as to be accessible to the roots of plants, the decalcifi- 

 cation of the soil actually helps the vegetation, by furnishing 

 the lime salts in solution. Hence (p. 143) the soils formed on 

 the limestone boulder-clays are more satisfactory than those 

 on the limestone-gravels. Sometimes the subsoil layer imme- 

 diately below a calcareous soil is found to be deficient in 

 calcium carbonate, which has accumulated again in the next 

 succeeding layer by downward percolation. 



Mr. Kilroe's second table (p. 147) is perhaps not set out so 

 clearly as it might be ; but it shows an elaborate series of 

 determinations of the amount of calcium carbonate, that is 

 regarded by him as available for plant food (p. 144) in different 

 siftings of each soil examined. Presumably sieves with cir- 

 cular holes were employed ; but it seems undesirable nowadays 

 to measure in fractions of an inch, rather than in decimals of 

 the metric scale. The material dealt with, and carefully sub- 

 divided into seven grades, is that with grains less than a quarter 

 of an inch in diameter. The mode of separation of the "silt 

 and finest sand " and the " finest silt and clay," the crucial 

 feature in the mechanical analysis of soils, should, we think, 

 be stated in all such records. The work done is an interest- 

 ing and hopeful reminder of that initiated by the Ordnance 

 Survey's geological branch under Col. Portlock about 1839. 



