1866.] GODWIN-AUSTEN BELGIAN TERTIAEIES. 233 



dimensions of the whole of the Crag series at Antwerp ; there is no 

 other place in Belgium where they are so thick — indeed, beds of the 

 true Scaldesien, Crag-like type, occur only at that place : it is also 

 the only spot where fossiliferous Diestien beds have been observed. 



The Diestien beds of Antwerp represent a condition of sea -bed 

 over which submarine Hfe is abundantly developed, and that with a 

 distinctive facies. Viewed in this way the sections from the Porte 

 de Tournhout are exceedingly interesting, presenting a rich and 

 varied fauna, of which a full enumeration has recently been given 

 by M. Nyst (Bull, de I'Acad. Roy. des Sciences de Belg. 1861, ser. 2. 

 t. xii. p. 20). One particular form, the Pectunculus glycimeris, 

 numerically exceeds aU others by 1000 to 1 ; it colonized this area 

 of the Crag sea, attaining a large size, and forming banks which in 

 places are not less than 2| feet in thickness. The Diestien was a 

 true life-zone, and exceedingly prolific, and as such it is in striking 

 contrast to the Scaldesien division, of which the whole of the as- 

 signed fauna is from dead and drifted shells: it may safely be 

 asserted that of the shells met with in the Scaldesien beds not one 

 lived where it is now found ; this, from a natural-history point of 

 view, is the real difference between the upper and lower Crag of 

 Antwerp. 



The area over which the Scaldesien shell-gravel and the fossili- 

 ferous Diestien ooze are to be seen together is even now so limited 

 that much generalization would be hazardous. Traced from below 

 upwards, the Antwerp sections show a gradual passage from very 

 fine and dark muddy ooze into sandy ooze, and finally into fine pale- 

 green clean sand ; in this there is a clear indication of a slight in- 

 crease in the moving powder of the water : a slightly diminishing 

 depth might cause such a change. The more sandy beds, where 

 they remain, form the uppermost portion of the Diestien division, 

 and contain but few shells. 



The Scaldesien division overlies an eroded surface of the Diestien, 

 and is found on every component portion of the series down to the 

 lowest and most compact beds. The line of separation is always to 

 be traced, and is mostly very distinct — it marks a sudden change of 

 condition ; — but as in the Diestien so in the Scaldesien series, the re- 

 arranged pale-green sands, brown sands with shells whole or broken, 

 the dead-shell banks, and uppermost the thickest layer of gravel with 

 pounded shells, indicate a progressive change and slow shallowing. 



The bathymetrical conditions indicated by the Scaldesien and 

 Diestien accumulations may be judged of by the guidance of the 

 soundings over the English channel ; the difference may have been 

 as much as from 30 to 40 fathoms, or to such an extent must the 

 crag -sea have shallowed about Antwerp from the time of the shell- 

 bearing Diestien beds, their denudation, and the formation of the 

 dead-shell sand and gravel bank. The Pectunculus glycimeris, the 

 most abundant member of the fauna, ranges from 25 to 60, and, 

 according to some, to 100 fathoms ; but no part of the Diestien beds 

 indicate a depth at which Dentalia become abundant and charac- 

 teristic, such as 80 to 100 fathoms. 



VOL. XXII. PAET I. S 



