328 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1917. 



7. IRELAND.i 



A tripartite division of the Irish glacial series has often been 

 claimed, and as often denied. That this division exists in the north- 

 east, east, and southeast of the country I am convinced, from an 

 exhaustive study of the literature, borne out by a few sections I saw 

 in 1914, but there is much question as to its meaning. The lower 

 bowlder clay, as described by Hardman (1875), is very tough and 

 marly, generally blue, gray, or reddish, with angular and rounded 

 blocks, a very considerable percentage of which is often made up of 

 erratics which have almost invariably, when their source of origin 

 can be recognized, been transported from the north or east. In 

 places they contain marine shells and Foraminifera. This bowlder 

 clay is of relatively rare occurrence. 



The so-called mid-glacial sands and gravels consist of a more or 

 less horizontal, stratified sheet of gravel with intercalated beds of 

 sand and clay. It is especially well developed in the central plain, 

 under the name of the " limestone gravels." The constituents of the 

 gravels are essentially those of the bowlders in the lower clay, even 

 including marine shells, but the relative numbers often differ. The 

 pebbles occasionally retain glacial striae, and large bowlders are not 

 infrequent. 



The mid-glacial gravels are in j)Iaces capped by the upper bowlder 

 claj', which is commonly looser and sandier than the lower, and often 

 brown in color ; the bowlders are similar to those of the lower clay, 

 with the addition of some from sources in a very different direction, 

 and also with a far higher percentage of local material. Marine 

 shells are almost entirely absent.- The upper bowlder clay is fre- 

 quently capped by gravel terraces and eskers. 



It is exceedingly rarely that any indication can be found either of 

 temperate interglacial deposits or of a great difference in age be- 

 tween two bowlder clays. The critical area is that of the " pre- 

 glacial " raised beach of the southeast. This, as described by W. B. 

 Wright and H. B. Muff (103), extends from Cork to Wexford at a 

 uniform level of about 10 feet above the present beach, possibly de-' 

 scending slightly toward Wexford. In level and in the general se- 

 quence of deposits it is so exactly similar to that of south Wales that 

 it is impossible to doubt their correlation, but there is one difference ; 

 in southeast Ireland the beach is overlain by two bowlder clays, sep- 

 arated by sands and gravels. The general sequence is: ' 



8. Upper "head." 



7. Upper, loose sandy, bowlder clay. 



6. Sands and gravels. 



1 In this section dates without numbers refer to Mr. Lloyd Praeger's Bibliography 

 (102). 



