10 MM. Rutot 8f Van den Broeck—Age of the ' Tvffeau de Ciply.' 



in the Co. Wexford. The rocks therein have not been claimed as 

 Laurentians by Dr. Hull, although some have been so classed by 

 Dr. Callaway. All the rocks are evidently portions of one group. 

 To me it would appear that unquestionably they belong to the 

 neighbouring rocks, which by their fossils are proved to be of 

 Cambrian age. 



The sole evidence for the existence of Laurentian rocks in Ireland 

 is the lithological characters of the rocks ; and if such characters 

 are of value, they ought to be of equal value in every case. This, 

 however, is not the case, as in many places rocks lithologically 

 more or less similar to the American Laurentians are left out in the 

 cold ; while in other places younger rocks, whose age is indicated 

 by their fossils, are included. 



III. — The Tuffeau de Ciply shown to be chiefly of Tertiary Age. 

 By MM. A. Exjtot and E. Van den Bkoeck. 

 'E wish briefly to state an important result, which the study of 

 certain Tertiary and Cretaceous beds in the neighbourhood of 

 Mons has enabled us to arrive at. 



For a long time past, the beds, well known in the district just 

 mentioned, by the name of Tuffeau de Ciply, have been considered 

 by all geologists to be the equivalents of the Maestrichtien, that is 

 to say, as belonging to the highest subdivision of the Cretaceous 

 series of Belgium. 



Now, our recent researches have convinced us that in the group 

 of beds called the Tuffeau de Ciply, there have been confounded two 

 series quite distinct from each other : 



A. A lower fossiliferous series of slight thickness, extremely rich 

 in characteristic Cretaceous species, amongst which may be men- 

 tioned specially Thecidium papillatum and Belemnitella mucronata. 

 We propose to give to this inferior tuffeau, which appears to cor- 

 respond to certain horizons of the Upper Cretaceous (Maestrichtien) 

 of Limbourg, the name of Tvffeau de /St. Symphorien, from the locality 

 where it may, at present, be best observed. 



B. An upper series, with fossiliferous zones, devoid of Cretaceous 

 species, 1 but containing, on the contrary, a fauna with a Tertiary 

 facies, including numerous forms identical with those of the Calcaire 

 grossier de Mons. This series, which attains a thickness of nearly 

 twelve metres, constitutes the type of the deposit known by the 

 name of Tvffeau de Ciply. Its base is formed by a conglomerate 

 called the Pvudingue de la Malogne, which, in certain localities, con- 

 tains numerous rolled Cretaceous forms derived from the underlying 

 formations. 



The preceding data have been derived from stratigraphical and 

 palseontological observations, which show, furthermore, that there 

 exists an insensible passage between the Eocene formation known 

 as the Calcaire grossier de Mons and the Tvffeau de Ciply, by the 



1 Nevertheless, two Maestrichtian forms, Thecidium long irostre, Bosq., an&Argiope 

 miavscopica, Schloth., have passed up into the Eocene Tuffeau de Ciply. 



