280 Mr, Lyell on the Strata of the Plastic Clay Formation in the Cliffs 



a bed of alluvial mud. The junction of the rivers Stour and Avon takes place 

 about half a mile below Christchurch, which is situated two miles inland from 

 Muddiford. There is a shifting- bar of sand at the mouth of the harbour at 

 Muddiford^ rendering the river so shallow that it can be forded at low water 

 during summer. Vessels drawing more than five feet water cannot enter. 

 Although there is no accumulation of alluvial gained land at the mouth of the 

 Stour and Avon, Muddiford stands on sand evidently thrown up by the sea, 

 and a trifling accession of soil is derived from this source. The ancient low 

 cliff is now clearly seen a few hundred yards inland, on the north of the village, 

 and the ancient sea-beach at its base forms the present road. 



For the space of more than a mile from the mouth of the Stour and Avon to 

 the east point of Christchurch Head, are hills of blown sand, through which 

 the storm of November 1824 broke wij:h great violence. The subjacent strata 

 are entirely concealed along this shore, and there are no means of filling up 

 this chasm in the section : but before arriving at the east point of Christchurch 

 Head a line of ferruginous sandstone concretions is seen on the beach, running 

 out to sea in a direction E. S. E. (See PI. XXX. No. 1. a.) At Christ- 

 church Head the regular section of the strata is first resumed after the inter- 

 ruption caused by the valley of the Stour and Avon. The strata then are as 

 follows, beginning with the uppermost: — 1st. Flint gravel, varying between 

 the east and west points of the Head, from 5 to 20 feet. 2dly. A very fine 

 whitish sand, varying in thickness from 8 to 20 feet. This sand, crops out a 

 little to theW. of West Point. (Pl.XXX. No. 1. b.) 3dly. Sand and loam vary- 

 ing in colour, generally greenish or grayish blue, in parts yellowish, or brown, 

 and often darkened by bituminous matter. (PI. XXX. No. I.e.) In these beds 

 of sand and loam are concretions of ferruginous sand, not unlike those of the 

 lower greensand or Shanklin beds, and others of clay-ironstone, resembling 

 considerably in appearance the clay-ironstone of the coal-formation : black 

 flint pebbles occur in some parts of the sand and loam, and sometimes in the 

 concretions. Parallel layers of these concretions, separated by beds of sand 

 many feet in thickness, first appear at the East Point, and increase from 2 to 5 

 in number as the strata rise towards the West Point. They are very conspi- 

 cuous, as the concretions are large, and stand out from the cliffs in relief, the 

 soft sand being removed from around them. 



A quantity of bituminized wood, and sometimes large flattened trunks of 

 trees occur in the concretions. One of these trees which I measured, was 

 four feet long and two and a half in circumference. The bark or external 

 coat of this fossil plant consisted of a black shining coal about a quarter of an 

 inch thick, the interior being filled with clay-ironstone. There is a large per- 



