146 Analysis of Scientific Books. 
the Strand, 200 feet; at White’s club-house, in St. James’s 
Street, 235 feet; at Chelmsford barracks 300 feet; and at 
Lord Spencer’s, at Wimbledon, the well is 530 feet deep, and 
it is doubtful whether the clay is actually there pierced. By 
indirect examinations, the greatest thickness of the clay in the 
London basin has been estimated at 1000 feet, but this is mere 
guess. The height to which the water rises in these wells will 
depend much upon their locality. Upon perforating into the 
strata whence it issues, it generally rushes forth with violence, 
and assumes an invariable level; and there are several instances 
of its overflowing in a perpetual stream, of which the well at the 
late Mr. Goldsmid’s, at Merton; that sunk by the late Mr. 
Vulliamy, at Norland-Hill, behind Holland-House, on the Ux- 
bridge road ; and that lately made at Ravenscourt, the seat of 
George Scott, Esq., at Hammersmith, may be quoted as 
instances. 
Above the blue clay we find, in certain situations, distinct 
superimposed strata; thus on the east coast of Suffolk low 
cliffs resting upon the London clay are found to consist of sand 
and gravel, enclosing peculiar fossils; the whole mass is known 
by the appellation crag. Of the shells which it contains, the 
greater number resemble the recent shells of neighbouring seas ; 
there are, however, a few extinct varieties, and among them 
the murex contrarius, or reversed whelk; though, what. is very 
curious, the fossil shell with the whirls in the ordinary direction 
is also found here. ‘ihere are likewise a few fossil bones, much 
impregnated with iron, and belonging to unknown animals. 
This formation is seen at Walton Naze, in Essex, and caps the 
cliffs on both sides of Harwich, extending considerably into 
Suffolk and Norfolk, where it forms a fertile soil. The sandy 
deposits which cover certain parts of the London clay, and 
which our authors denominate Bagshot sand, must also be con- 
sidered among the deposits which geologists have lately termed 
the Upper Marine formation. Bagshot Heath, and the sand of 
Hampstead and Highgate, are of this description. It is, how- 
ever, in the Isle of Wight that we meet with the most interesting 
series of the strata above the blueclay. For our knowledge of 
the curious arrangements and alternations of this district, we 
are exclusively indebted to the accurate and industrious re- 
searches of Mr. Thomas Webster, one of the Secretaries of the 
Geological Society. The cliff called Headen Hill, on the north- 
west coast of the island, exhibits an admirable section of these 
formations. This hill consists of several strata: the uppermost 
overlies the upper marine formation, and contains abundance of 
fresh water shells without any admixture of marine exuvie, 
together with seeds of a flat oval form, and parts of coleop- 
terous insects; it has been termed the upper fresh-water for- 
mation, and may be seen in many other parts of the island, es- 
