16'> The Aynerican Geologist. Scptcini).-!-, isoe 
v.illcy at this stage. The cskor was a])i)areiitl_v formed in a 
channel in tiie ice, tiie soutiieni part oC which was prf)])al)1y 
arched over, while the wide northern portion was, at least in 
its later stages of growth, open to tlie chiy. The ice-sheet had 
disappeared from the hills on the west and lay in the valley 
as a mass so narrow as to allow on the west the formation of 
washed deposits back of Lonsdale and on the east a similar 
terrace on the site of Valley Falls. This is the most distinct 
of the frontal deposits formed at this stage. Probably the 
extensive sand-plains east of the Blackstone river in the towns 
of Pawtucket and Attleboro and along the line of the Old 
Colony railroad belong to this time, or to a somewhat later 
stage of the retreat. 
Sand-plains between Providence and Boston. 
Northward there are belts running northeast and southwest 
along which sand-plains with ice-contacts occur. Attleboro, 
Mass., is located on such a plain; so also is Mansfield; north 
of this is the Sharon plain; and there is another northeast of 
Canton Junction, and one at "Readville, — all being in Massa- 
chusetts, on the line of the Old Colony railroad between Prov- 
idence and Boston. In general, it may be said that the sand- 
plains described as occurring between Point Judith and Prov- 
idence are parts of a succession of morainal and washed 
deposits which are traceable eastward and northeast toward 
the interlobate axis which passes up the western shore of 
Cape Cod bay toward Scituate. Mass. In another paper I 
hope to present a map of these retreatal deposits. 
The Space between Stages of Retreat. 
The several stages of retreatal deposits in the Narragansett 
bay region, from near Wickford northward, manifest a ten- 
dency, in the ice-front, to be bordered by sand-plains at inter- 
vals of about one mile. This regidar recurrence of a halt in 
the ice-front with sand-plain building calls for an explanation, 
but it does not appear evident to the writer what processes 
brought about this sequence. It is apparent that the interval 
is not connected with seasonal changes. Davis has shown 
that during the growth of the Woodland sand-plain, near Bos- 
ton, the ice-front did not melt back more than a few j^ards 
during the outward extension of a delta to the distance of 
two or three hundi-ed yards. It is reasonable to suppose that 
