168 GEOLOGY OF TIIK ISLE OF WIGHT. 



quently of a bright green colour, like many of the 

 layers of marl and clay at Hordwell. Detailed 

 descriptions of the strata and their fossils are 

 given by this eminent geologist in the second 

 volume of the Geolog. Trans. ; the following sum- 

 mary will be useful to the visitor : — 



1. Alluvial gravel, forming the top of the cliff; composed of 



broken chalk-flints, with interspersions of sand and marl ; 

 thickness from 5 to 50 feet. 



2. Fine white sand with greenish marl ; — from 3 to 12 feet. 



3. Green marls, with arenaceous clays ; — 16 feet. Contain 



bituminous wood and seed-vessels, with shells of the 

 genera Helix, Unio, Melanopsis, Planorbis, and other 

 lacustrine species. The lowest stratum is laminated marl, 

 with layers of Cyprides. 



4. Sands and clays; — 15 feet. Numerous shells of the mya 



V' garia. Lignite occurs in a layer of bituminous clay. 



5. White calcareous marl, largely constituted of aggregated 



freshwater shells; contains gyrogonites (see p. 109). It 

 rests on a layer of black carbonaceous clay, with lignite; 

 1 foot. 



6. Green unctuous and arenaceous marls ; the lower portion 



consists of beds of pure white sand, with argillaceous 

 sands;— 15 feet. Numerous fluviatile shells. The white 

 sand contains abundance of the shells of a small mussel 

 (mya plana) in a very perfect state. 



7. Light green calcareous and sandy marls, with layers of a 



carbonaceous clay containing lignite; — 22 feet. Nu- 

 merous shells; and seed-vessels. 



8. Green marl, carbonaceous clay and lignite, ferruginous clay, 



marl with r<</<hi/i/< imi>nssions, and green clay; 

 It feet. Freshwater shells, principally two or throe 

 species of bivalves. 



