282 Mr. Lyell on the Strata of the Plastic Clay Formation in the Cliffs 



beyond Double Ditches, consisting of diluvium from 8 to 10 feet thick, covered 

 with blown sand from 3 to 5 feet deep. Agriculture in the neighbourhood of 

 the coast between this spot and Boscomb suffers much by this covering of 

 blown sand. At the foot of the low cliff above mentioned the regular strata 

 are seen at a few points ; first white sand with ferruginous yellow streaks, then, 

 at a place called White Pits, reddish brown clay (PI. XXX. No. 1. h.), then, 

 sand with much vegetable matter. Beyond this to the westward is white sand 

 at intervals, with layers of white decomposed flints extremely light. About a 

 mile beyond White Pits, a bed of sand containing much bituminous matter is 

 seen at the foot of the low cliffs, after which the cliffs rise again to 40, and 

 soon after to 60 feet in height. The cliffs, when they first rise, consist of 

 white and yellow sand 18 feet thick, and white sand below with a brown 

 thinly laminated clay 10 feet thick (PI. XXX. No. 1. i.) ; the whole capped 

 with 12 feet of gravel. 



From this point to the Flag-house near the mouth of Pool Harbour, a di- 

 stance of about 8 miles, the section presented by the cliffs is continued so pre- 

 cisely in the line of bearing of the strata, that no new beds rise up ; and it is 

 unnecessary to describe it in detail. It will be seen by the accompanying 

 section that the cliffs are intersected by numerous valleys and chines, the 

 principal of which are Boscomb Chine and Bourn Mouth. The prevailing 

 character of the strata throughout this extent of coast is fine white sand ; but 

 yellowish and pinkish beds of sand occur, and thinly laminated clays in great 

 abundance, resembling in appearance many of the light coloured argillaceous 

 marls of Montmartre near Paris : but in none could I discover any organic 

 remains, except vegetable impressions, and these very indistinct. The lower 

 sands of this series are frequently ash-coloured, apparently from the admix- 

 ture of vegetable matters, with which they are charged very irregularly, and 

 they consequently often change colour suddenly. Black bituminous clays are 

 sometimes associated with the ash-coloured sand ; as for instance to the east of 

 Boscomb Chine, where, in the lower part of the cliff, ash-coloured sand 15 feet 

 thick appears, with 25 feet of black clay below it. Similar dark beds occur 

 to the east of Bourn Mouth. The following is the section of the cliffs at " The 

 Chines " near Boscomb Chine. 



Gravel 25 feet 



White ^-ellow and pink sands 60 



Ash.coloured sand wi(h vegetable matter ... 25 



Pipe-clay is seen in a few spots, as at the foot of the cliff to the east of 

 Boscomb, and west of Big Durly Chine. I was informed also that pipe-clay 



