190 Correspondence. 
a part, and not the whole system of Kaims. In Ireland the Esker 
systems extend sometimes for over a hundred miles, but are modified 
by local circumstances. On low ground they are well defined 
ridges, which break into Shoal-eskers (consisting of irregular 
mounds and short ridges), crossing high ground, but again be- 
coming well defined when the high ground is passed. If a hill 
occurs, the Esker will be either deflected and form a Fringe-esker 
round it, or there will be a break in the Esker system, as it ends ~ 
on or near one side of the hill, but sets on again at the other side. 
The Esker-drift seems to be washed Boulder-drift, or ‘ Post-drift 
Gravels ;’ and in sections which expose the two kinds a well-marked 
line of demarcation will be observed between them, which would 
seem to prove that they are different kinds of Drift. Of course if 
the ‘ Post-drift Gravels’ were formed by the washing of the Boulder- 
drift, we shall not always find the latter entirely washed, as some- 
times the washing power would not have been strong enough ; and 
in these places the two kinds of Drift would seem to blend one 
into another. This is not the proper place to examine the ‘ Post- 
drift Gravels;’ but where they are well developed they always have 
a marked boundary. In the basal beds of an Esker, or in an Esker 
in which the gravel is unstratified, blocks will be found that are 
striated and polished ; but this does not prove that they are of the 
same age as the Boulder-clay; since these blocks may have been 
polished before they were removed from the Boulder-clay, and were 
not afterwards rolled enough to obliterate the old marks. That 
this is the case seems likely, as the marks on them are not nearly 
as fresh as if they were taken direct from a bank of Boulder-drift. | 
I would suggest to observers that they should trace Kaims or 
Esker Systems across a wide expanse of country, and that they 
should carefully note the different changes that occur ;—what effect 
high land has on the Esker Systems; what is the height of the 
Jand on which they are in well defined ridges; what the height 
when they break into Shoals ; when they break into shoals, is the 
Drift ‘ Post-drift Gravels’ or Boulder-drift, denuded into ridges and 
mounds, or partly one and partly the other? They should also note 
carefully all junctions between the two kinds of Drift. The ‘Post- 
drift Gravels’ sometimes form a gently undulating country, and do 
not break into ridges; and an observer ought to be careful not to 
confound it with a much older gravelly Drift which underlies the 
Boulder-clay (the Drift of the country before the Glacial Period), 
for which I would propose the name ‘ Preglacial Drift.—Y ours, &c., 
3 G. H. Kinanan. 
EXELISSA v. KILVERTIA. 
To the Editors of the GEOLOGICAL MAGAZINE. 
Mr. Lycerr* has given to Cerzthia having an entire aperture the 
generic title of Kdlvertia; and has referred C. strangulatum, D’ Arch., 
* Supplementary Monograph, Moll. Great Oolite, p. 98. 1863. 
