224 J. G. Goodchild—On ‘“ Overlap,” ete. 
arisen from the destruction of an underlying bed. But ] am not 
prepared to admit that none of the stools are in situ; for it has not 
been proved. Considering the rottenness, and the very spongy 
nature of the rootlets even in the Post-Glacial Forest-Bed trees, I 
am not surprised that, in this much older bed, the author of the 
memoir has so often failed to detect the “smaller fibres” he has so 
assiduously looked for, but would not 20 feet in diameter of roots 
satisfy most men ? 
One more observation before I conclude. A map is given, p. 57, 
showing “the Rhine Estuary during the formation of the Cromer 
‘Forest Bed.’” The materials on which this is based are of the 
slightest, which criticism is perhaps applicable to the generality of 
such maps. Considering that the Forest Bed is at about the same level 
as the present mouth of the Rhine, and that they are in a direct line 
about 120 miles apart, that the basin of the German Ocean inter- 
venes, that the rivers on the east coast, including Norfolk, are even 
in their Post-Glacial beds much below the sea-level, that the bed of 
the Rhine is far below its modern delta, that the solid chalk is seen 
now on the Norfolk shore and immediately underlies the Forest Bed 
in places, and in others is not far off, and the author does not assume 
“any tilting or disturbance in beds of so recent a date unless such 
can be clearly proved.” Considering all these difficulties, it would 
surely have been well—if they occurred to the author—to have dis- 
cussed them. But I suppose the bringing of the Rhine to Norfolk 
is the necessary outcome of the author’s view of the mode in which 
the trees have been deposited. Such unfortunately, on very little 
provocation, are the liberties taken with physical geography. 
VI.—On “OvertaP” AND 1Ts RELATED PHENOMENA. 
By J. G. Goopcniup, Esq. ; 
of H.M. Geological Survey. 
T must be sufficiently obvious to the readers of the GEoLoGIcAL 
Macazine that any modification of the original meaning of a 
descriptive term that may serve the purpose of enabling us to 
convey a specific idea with less chance of ambiguity is a distinct 
gain to both author and reader. This is especially the case when 
other specific terms are forthcoming to fill the vacancies in descrip- 
tive terminology caused by the restriction in meaning of the term 
in question, and when it is possible at the same time to supply a 
suitable generic term sufficiently comprehensive in its meaning to 
embrace the common characteristics of the whole. 
Every now and then local exigencies in the treatment of some 
special subject require a writer to employ a term in a signification 
somewhat more limited than it had been customary to give to it 
before. If the applicability of the term in its modified sense to 
similar cases of a less general and specific character are perceptible 
to other workers in the same field of research, it would seem much 
more advantageous to give the specialized form recognition by ° 
employing it, a8 occasion arises, than to lose the opportunity of 
