J. S. Gardner — Correlation of the Tertiary Series. 149 



strata appear due to purely freshwater action. Before I proceed 

 further, I may as well at once meet an objection that may be urged 

 against the purely freshwater origin of the Lower Bournemouth 

 Series, that is, the occasional presence of Teredo-bored wood in it. 

 This isolated fact for some time presented a grave difficulty, but in 

 addition to the evidence recapitulated in Dr. J. Gwyn Jeffreys' account 

 of the occurrence of similarly bored logs 300 hundred miles up the 

 river Gambia, and his distinct statement, to which I have before 

 alluded, 1 that there is a species which lives in fresh-water; the 

 mention of the subject elicited letters containing even stronger testi- 

 mony as to the fresh-water habits of the ship-worm. In one of 

 these 2 Arthur Nicols states that Teredo navalis is certainly able to 

 endure a long continuance of fresh water, being found at Brisbane, 

 where the river is subject to long-continued freshets. One of these 

 lasted ten days, during which the flood was so powerful that ocean 

 steamers could not get up, yet although the river at ebb-tide is more 

 fresh than salt, the piles have to be protected. In the previous letter 3 

 a correspondent states that in the Delta of the Irawadi, where for 

 eight months in the year the waters are only slightly brackish or 

 even potable, the large canoes which traverse them are infested with 

 ship-worm, and have to be fired to get rid of them. 



This difficulty may, therefore, be regarded as finally removed. 



The Lower Marine Beds are black sandy clays, and contain oysters 

 and leaves, covered with Polyzoa, and a variety of casts of shells, 

 apparently referable to Bracklesham species ; Gallianassa is also 

 abundant in them, and shore-crabs are met with. These dark beds 

 can be traced from this point for about five miles, where they dip 

 under the beach. They change over and over again, occasionally 

 very abruptly, within short distances, from dark sandy clay to buff 

 or yellow or white sand. Sometimes the dark clay suddenly thins 

 to a mere layer, or is still more frequently only represented by 

 small lenticular patches. The junction between the dark beds and 

 those which overlie them can nearly always be traced by a line 

 of wet which darkens the lower series, even if they also happen 

 to be of white sand. Above these are the Upper Marine Beds, 

 generally of pure white, sometimes slightly yellow sand, and 

 inclosing masses of well-rolled shingle. The pebbles are sometimes 

 large, but, of whatever size, they always have a thick white coating. 4 

 so much so, that frequently only a nucleus of black flint, or not even 

 that, remains. These Eocene pebbles cannot be mistaken for those 

 of the overlying gravel, being far more worn, and well rounded. 



These Lower Marine Beds contain plant-remains of great interest. 

 Going back to the Fern Beds, 5 which are high in the cliffs, the greatest 

 difficulty is experienced in ascertaining how the freshwater beds 

 came to be so completely replaced, within only 100 yards, and upon 

 the same horizon, by marine beds. The frequent landslips, indeed, 



1 Proc. Geol. Association, vol. v. p. 55. 



2 " Nature," May 3rd, 1877- 3 "Nature," April 19th, 1877. 



4 As the Bracklesham flint-pebbles are usually encrusted with Litharea Websteri, 

 probably this may explain the " wbite coating." — Edit. Geol. Mag. 



5 The uppermost of the Bournemouth freshwater series. 



