Perry. ] 56 [February 28, 
Of the three general terms in the left hand column, two require — 
an explanation. “Holocene” is proposed in conformity with the 
“ Plistocene,” etc., of Sir Charles Lyell, as descriptive of the times 
which he calls Post-Pliocene, during which all the Molluscan species 
were recent in the sense that they belong to the Post-Tertiary, 
though not necessarily in the sense that they all are now actually 
living. Probably a few of the Plistocene species of Mollusks are 
extinct. It is possible, as many have asserted, while, as others affirm, 
it is as yet by no means certain that some of the species are prop- 
erly Tertiary in their character, they having simply survived the 
age of which they are more chiefly characteristic. The other term 
requiring explanation, “ Autocene” is introduced into the table, in 
the place of “ Recent ” or ‘ Present,” merely for the sake of uniform- 
ity. Were it desirable to extend the nomenclature of Sir Charles 
Lyell, this term might be conveniently substituted for “Recent,” 
Autocene meaning, as the etymology of the word suggests, the ,em- 
phatically new, and thus appropriately designating the latest times. 
On the subordinate divisions a word may be necessary. The Plisto- 
cene consists of two stages closely akin, but very distinctive in their 
characteristic marks, the Ice or Glacial period, and the Terrace 
period. Of these terms, the latter, though not altogether appro- 
priate as it has been ordinarily used, is inserted in the table for want 
of a better. It is perhaps also best to look at the Holocene as com- 
prising two closely related sections of time: viz., (1) the Marl period, 
in the course of which there was a marked prevalence of ponds, in 
which the remains of fresh water Mollusks were deposited; and (2) 
the Peat period, during the continuance of which the growth and 
deposition of swamp mosses were characteristic processes. Until 
something more definite is made out, the Recent may be conveniently 
looked at under two subdivisions, viz., the Prehistoric and the His- 
toric, just what ground the Ages of Stone, of Brass, and of Iron 
will eventually cover being as yet uncertain. 
As these several subdivisions are to be now taken up in their 
chronologic order, I proceed to notice, 
IV. THE PLISTOCENE TIMES. 
New England is covered with a superficial, unconsolidated mass 
of matter, which is very characteristic. The lower part, which 
usually rests directly on the underlying solid rocks, consists of het- 
