XVIII. — Oil the Strata of the Plastic Clay Formation exhibited in the 

 Cliffs between Christchurch Head, Hampshire, and Studland Bay, 

 Dorsetshire. 



Bv Charles LYELL, Esq. F.R.S. P.L.S. F.G S. 



[Read March 17th, 1826.] 



1 HE range of coast between Christchurch (or Hengistbury Head)^ near Mud- 

 diford in Hampshire^ and the southern side of Studland Bay in Dorsetshire, is 

 nearly 17 miles in length. It presents fewer geological phaenomena of interest 

 than its extent might have led us to expect; but a detailed examination of these 

 Cliffs serves to complete the history of our Southern Coast, of which so large 

 a portion is now illustrated by memoirs published in the Transactions of the 

 Geological Society. 



The strata about to be described belong exclusively to the plastic clay for- 

 mation ; and it is necessary to premise that the uppermost bed of this forma- 

 tion is seen to the East of Muddiford. In an account of the strata between 

 Hordwell Cliff, and Muddiford, published in the last volume of the Society's 

 Transactions, Mr. Webster has referred the sand that rises from beneath the 

 London Clay at the western extremity of Highcliff, about a mile to the East of 

 Muddiford, to the plastic clay-formation. In this sand he observed fragments 

 of lignite, and branches and leaves of plants. Not far from the spot where it 

 rises, it is cut off by denudation, the valley of the Stour and Avon here reach- 

 ing the coast ; and the interval between this and Muddiford is covered up 

 with gravel and blown sand. A great quantity of fossil wood retaining the 

 woody fibre in a remarkably perfect state is thrown up by the sea on the 

 beach at Muddiford, and indicates an abundance of these remains in the strata 

 there, acted upon by the powerful current that sets in round Christchurch 

 Head. The force of this current carries away the materials brought down 

 into the estuary of the Stour and Avon, and entirely prevents at Muddiford 

 that gain of land so common at the mouths of rivers. In the bottom of the 

 valley higher up, between Muddiford and Christchurch, the river has deposited 



VOL. II. — SECOND SERIES. 2 O 



