155 Tue Rey. MAXweLu H. CLOSE, 
Upper Boulder Clay.—Over the generally well-washed and 
stratified Middle sands and gravels may sometimes be seen a 
nearly, occasionally quite, unstratified deposit, which we may 
call the Upper Boulder Clay, without implying thereby that it 
has been formed in the same way as the Lower Boulder Clay. 
It is of a looser, more earthy material, and may contain far- 
travelled stones. But as the nature of this deposit, if it be 
really a separate one, is obscure, and there is considerable differ- 
ence of opinion thereanent, and as entering into controversy 1s 
outside our present business, we shall pass on to the next. 
Eskers.—These seem to be the latest of these drift accumula- 
tions. We shall not now go into the difficult and vexed question 
of their mode of formation. They must be as old as the time of 
floating ice, as they sometimes have very large transported 
blocks lying wpon them, just as the level drift often has. It is 
sometimes evident that these have not been brought out by 
denudation, but that they have been dropped on the esker by 
some agency that did not interfere with the gravel and sand 
already there; and the only agency that can be suggested is 
floating ice. The eskers consist of thoroughly well washed and 
generally stratified materials. Shell fragments have been found 
in them, but only in one or two instances, As their name implies, 
they are generally in the form of ridges, though they are often 
but more or less well-defined irregular mounds. There is a good 
specimen of a ridge esker at Greenhills, a couple of miles W. of 
Rathfarnham. Its whole length is nearly three miles, and its - 
height from thirty-five to sixty feet. A road runs along the 
crest of its southern portion, where it is narrower and well-defined, 
for a length of two and a quarter miles. There is also a ridge 
esker at a place thence called Esker, on the S. side of the Liffey, 
six miles W. of Dublin, and there are irregular esker mounds in 
Stillorgan Park and elsewhere. — 
Local Glaciation.—This is doubtless the proper place in which 
to mention the glacial moraines which are to be found among the 
hills in the neighbourhood of Dublin. It is most probable that 
those moraines were finally left by the ice, as we now see them, 
about the time of the formation of the eskers or shortly after that. 
Kach of the two Loughs Bray (12 miles 8. by W. from Dublin) 
occupies its own division of a laterally double hollow on the N.E, 
side of Kippure Mountain (granite, 2,473 feet above the sea). The 
