Geological Society. 291 
Simia Linn., now alive in the collection of Exeter ’Change, 
allied to, if not identical with, the Simia Lagothrix of Baron 
Humboldt; by Edward Griffiths, Esq. F.L.S. 
GEOLOGICAL SOCIETY. 
March 17.—A paper was read, entitled, “* On the strata of 
the Plastic Clay formation exhibited in the cliffs between Christ- 
church Head, Hampshire, and Studland Bay, Dorsetshire ; 
by Charles Lyell, Esq. F.G.S. &c. 
The strata of sand and clay which form the subject of this 
communication are referable exclusively to the plastic clay 
formation. They occupy an interval in the coast of about 16 
miles in extent, between the London clay of Highcliff on the 
east of Muddiford, and the chalk of the Isle of Purbeck. A 
coloured section of the strata exhibited in these cliffs accom- 
panies the paper. The author first describes in detail the cliffs 
of Christchurch, or Hengistbury Head, which consist of sand 
and loam, often much charged with bituminous matter, and 
containing large concretions of ferruginous sandstone and clay 
ironstone, disposed in fine parallel layers, in which, as well as in 
the sand and loam, occur black-flint pebbles, lignite, and flat- 
tened impressions of fossil trees. Below these strata are dark 
bituminous clays, alternating with red and brown sands, and 
with occasional layers of black-flint pebbles. After the outcrop 
of the above strata, the cliffs are low, and about three miles from 
Muddiford are composed solely of diluvium. When they 
rise again in height, their direction corresponds with the line 
of bearing of the strata, so that the same beds are continuously 
exposed for eight miles, as far as the mouth of Poole Harbour. 
These beds consist of fine white sand, pinkish sand, and 
thinly laminated argillaceous marls, containing occasionally 
much vegetable matter ; and the whole series exceeding 150 
feet in thickness. ‘The section is interrupted for a space of 
21 miles by the mouth of Poole Harbour and the bars of sand 
on each side of it. But in the cliffs near Studland the strata 
are again seen, consisting principally of yellow and purplish 
sand, white sand alternating with thinly laminated white clay, 
and sand with ferruginous concretions passing into sandstone, 
and pipe-clay. 
The junction of the chalk with the superior strata is very 
indistinctly exposed, but a thin bed of striated soft chalk-marl 
rests immediately upon the chalk, as is the case in Alum Bay. 
The author concludes with observations on the diluvium of 
this district, composed chiefly of chalk-flints ; and he infers from 
its local characters, both here and in the rest for Hampshire, 
as well as in the district between the North and South Downs, 
202 that 
