THE MUD OF MILFORD HAVEN. 29 



deposits. VV^lierever excavations for building or other pur- 

 poses are going on near the banks of a tidal river, there will 

 be found an ample field for the industrious observer. 



At Swansea, for instance, where some docks are now being 

 constructed, 1 have obtained some rich samples of Diatoma- 

 ceous clays. 



The strata through which these excavations are being made 

 occur in the following; order : — 



Total . . 25 



The lowest bed of this clay, at 25 feet depth, is literally 

 "swarming" with Epitlieviia musculus and Surirella striatiila : 

 other marine forms are abundant ; while the fact of two beds 

 of peat lying above it shows its extreme antiquity. The 

 other two beds of clay above it, marked D D, are also rich in 

 Diatomaceous remains. I have not yet had time to examine 

 these deposits thoroughly, so as to make lists of the forms 

 occurring in them ; but a comparative examination of the 

 three beds would be highly interesting, and I hope to be able 

 to prepare one for the next number of this Journal. 



Again, from a brick-yard near Carmarthen, which is now 

 upwards of a hundred yards from the present banks of the 

 river (the To wy), and at a depth of about five feet below the 

 surface of the ground, I have obtained a sample of the old 

 tidal deposit which now forms the brick-earth, and which is 

 full of the most magnificent specimens of Triceratium favus 

 and Coscinodiscus that I have ever seen ; while the beautiful 

 Actinocyclus i^edenarius, with its sixteen septa, is of common 

 occurrence. 



From the foundations of a bridge we are now building 

 over the Cleddan near this town (Haverfordwest), I have also 

 obtained a rich sample of clay at a depth of about 10 feet, 

 and at about 20 feet distance from the present bank of the 

 river. In this sample the fresh-water forms occur more fre- 

 quently than in the other deposits. This might be expected, 

 as the tidal influence does not extend very far above this 

 point. 



1 could enumerate many other instances which have come 

 under my notice, but it would be only a repetition of the 



