Ixxiv PROCEEDINGS OF THE GEOLOGICAL SOCIETY, 



species of mammals, one fish, nine land and freshwater shells (which, 

 although so fragile, are preserved entire), and traces of plants. 

 Beneath this the beds contain marine remains, amongst which are 

 ten recent species of shells. With these are associated a con- 

 siderable number belonging to the Campinian, Tongrian, and Brux- 

 ellian Systems of M. Dumont, the Crag of England, and the Cal- 

 caire grossier. The author arrives at the conclusion that this great 

 mass of sand and clays, as well as the lower sands of Amsterdam, 

 belong to the Campinian system of Belgium (or our Crag), and that 

 the upper beds belong to the Lehm period of the Rhine. Further 

 examination is necessary before we can conclude that this opinion is 

 correct. 



In the island of Urk in the Zuyderzee, M. Harting discovered a 

 low hill of diluvial clay full of fragments and boulders of the older 

 rocks, some two metres in diameter- — all rolled. Many of them belong 

 to the rock-masses of Scandinavia, and others to those of England and 

 Scotland. The author contrasts this with the deposits from the south 

 of Amsterdam and Gorinchem, the debris of which he considers solely 

 derived from the hills of the Rhine and the Ardennes. He also 

 touches upon the subject of the gradual subsidence of the land in 

 Holland, and considers the fact of the base of the peat being two to 

 three metres beneath the present mean sea-level, a strong proba- 

 bility in favour of this ^iew. There are indications of this subsi- 

 dence being at the rate of two inches in the century. iVt his sug- 

 gestion a Commission has been appointed to inquire into and deter- 

 mine this question. 



M. Hebert has also communicated (Bulletin, p. 419) a notice on 

 the " Plastic Clay" of Paris, and its relations to the beds in the north 

 of the Paris basin. The puddingstones of Nemours, which attain 

 a thickness of thirty or forty feet, he now agrees with M. de Roys 

 (p. 453) in placing at the base of the Tertiary series, and he con- 

 siders them to result from an extensive denudation of the chalk and 

 calcaire pisolitique which took place after the deposition of the Rilly 

 beds. The mottled and pure plastic clays which next succeed, form, 

 according to this author, a distinct and separate zone, always under- 

 lying the fausses glaises and the lignites of the Soissonnais ; and in 

 this respect these mottled clays would differ from those in this 

 country, which Mr. Prestwich has shown to be intercalated with the 

 lignites and fossiliferous sands. The upper sands of the Soissonnais 

 are, as it is well known, wanting in the neighbourhood of Paris. 

 He then proceeds to show what were the conditions under which 

 this series of beds were deposited, and remarks that probably large 

 brackish water lagoons extended from Paris to Reading and Brussels, 

 among which were here and there freshwater lakes of greater or 

 less extent. He offers no positive theory to account for the origin 

 of the pure plastic clay, but suggests that it may possibly have been 

 ejected in the same way as the gypsum beds. On this, however, he 

 does not insist. 



M. d'Archiac and M. de Roys differ on this subject from M. 

 Hebert. 



