JUNE 28, 1901.] 
the associated anticline of Weymouth, are 
treated in a chapter by Strahan (‘ The Geology 
of the Isle of Purbeck and Weymouth,’ Mem. 
Geol. Sur. England, 1898, pp. 280-235). Next 
inland lies the unsymmetrical Hampshire syn- 
clinal basin of Tertiary strata, broadening 
eastward, and thus analogous to the London 
Tertiary basin. Each basin gave rise to an 
east-flowing axial consequent river, the lower 
Thames and the Frome; but while the valley 
of the Thames is still well preserved, the 
southern side of the original Frome valley has 
been greatly consumed by the sea. Lateral 
consequents of good size still come from the 
north, and one of them, the Stour, rises back 
of the chalk cuesta; but nearly all the conse- 
quents on the south have been shorn off ; yet 
two small ones still remain, one on the Isle of 
Wight, one on the Isle of Purbeck, and each 
of these streams, like the Stour, heads back of 
the chalk, which on the south forms a mono- 
clinal ridge of nearly vertical structure. Much 
of the original axial consequent has been de- 
stroyed; the river now called Frome being 
only the upper 30 miles of a stream that may 
originally have had a length of over 100 miles. 
The Solent estuary, separating the Isle of 
Wight from the mainland, is taken to be a 
middle part of the axial consequent, as de- 
scribed by Strahan in an earlier memoir (1896). 
The Isle of Portland, south of Weymouth, is 
a smaller fragment of the devastated anticline, 
west of the other remnants. It is now con- 
nected with the mainland by the famous Chesil 
bank (Jbid., pp. 203-209), asuperb reef of peb- 
bles and sand, 18 miles long, enclosing a shal- 
low lagoon called the Fleet (from Saxon, mean- 
ing shallow water) for 12 miles. The exposed 
(southwest) face of the reef is a steep beach, 
benched with long, even terraces (locally called 
“curbs’), the temporary records of the maxima 
in an irregular but generally decreasing series 
of wave efforts; the highest crest of the reef 
being the work of the master storm of the de- 
cade or century. The reef rests on clays which 
are sometimes exposed on the beach face after 
storms. Pebbles are abundantly thrown over 
the crest of the reef during on-shore winter 
gales; the windows of the nearest houses in 
Chiswell (where the reef joins the Isle of Port- 
SCIENCE. 1033 
land) must then be boarded up, even though 
the crest is there 42 feet 9 inches above high- 
water mark. The reef as a whole must be 
marching slowly inland (northeast). It may 
have been formed originally several miles to 
seaward of its present position. The pebbles 
are largest at the southeastern end, where the 
reef is attached to the wasting and beach- 
less cliffs of the Isle of Portland, and finest to- 
wards the northwest end, where it approaches 
but does not reach the Chalk uplands of Brid 
port; yet the commonest pebbles are not de- 
rived from the Portland sandstones, but con- 
sist of well-rounded chalk flints ; and there are 
occasional Triassic pebbles, although no Trias- 
sic rocks are exposed for some 30 miles to the 
west. An earlier writer suggested that the 
movement of pebbles on the beach is from the 
northwest, and that the largest ones are now 
at the southeast end because they are most 
readily carried by storm waves and drift; but 
this is difficult to believe. Prestwich thought 
that the movement is to the northwest. Stra- 
han seems to accept the earlier opinion, but 
concludes that the more persistent movement 
is only inward (northeast); and that the ma- 
terials of the reef represent the most durable 
sweepings of the land area that has here- 
abouts been destroyed by the sea. Thus ex- 
plained, it seems probable that the chalk 
flints and the Triassic pebbles were derived 
from exposures of these formations somewhere 
along the original position of the reef, a dis- 
trict now occupied by the northwestern part of 
the English channel. 
5 6 es 
ee 
oF WIGHT 
ax Nv ISLE or NN le 
Vz. [) PoaTLAND =NGLI SH Cig San 
Part of southern England, representing the Hamp- 
shire syncline and fragments of the adjoining anti- 
cline. Chalk, blank ; older formations, lined ; Ter- 
tiary, dotted. 
