1866. | Geology and Palexontology. 417 
arrived at the equator. Before we had to deal with a sphere having 
no tendency to revolve on one particular axis more than on another ; 
but now there is resistance to be overcome—a resistance intensified 
by the rotatory motion of the sphere. So, in the case of the 
oblately spheroidal earth, for a mountain-mass to affect the axis 
of rotation it must possess a centrifugal force sufficient to over- 
come the resistance presented by that of the greater protrusion of 
the earth at the equator, that protrusion being equal to a belt 64 
miles thick at the equator. 
For some months past geologists have been awaiting with 
curiosity the publication of the details of an alleged discovery of 
Bracklesham fossils in beds beneath the Landénien inférieur 
(Thanet sands) of Belgium. It was felt that if this discovery 
were really such as it was represented to be, the “Colony” prin- 
ciple must be admitted as an essential element of uncertainty in the 
determination of the age of a stratum from the evidence of its 
fossils. Now that MM. Cornet and Briart’s paper has been pub- 
lished,* we are in a position to judge of the value of the evidence 
on which this asserted discovery rests. It appears that a well- 
section at Obourg, near Mons, revealed sandy beds underlain by 
limestones, and that these limestones yielded twenty-two species of 
Bracklesham (Calcaire Grossier) fossils, with about 120 others, 
mostly new. The sandy beds are considered to be identical with 
those near Angres and Tournay, which yield Pholadomya 
Koninckii, and are therefore of Landenian age. The proofs of 
this identity rest partly on a certain amount of lithological corre- 
spondence, and partly on sections which seem to prove the unin- 
terrupted continuity of the strata from one locality to the other. 
But it does not appear that Pholadomya Konincki has yet been 
obtained from the same section as the Bracklesham fossils. After 
an endeavour to weigh this evidence impartially and without 
prejudice, it appears to us that the following is a fair conclusion :— 
The evidence would be sufficient to establish, until disproved, the 
position assigned to these fossils by MM. Cornet and Briart, if no 
violation of previously received geological principles were involved ; 
but, under existing circumstances, this Tertiary “colony ” cannot 
be considered authentic until Pholadomya Koninckii, or some 
equally conclusive fossil, has been found in direct superposition to 
the Bracklesham shells. Even then the case would seem to be as 
good for an extension of the range of Pholadomya Koninckit as for 
the “ Calcaire Grossier ” colony. 
The ‘ Geological Magazine’ for the past three months contains 
* “Note sur la découverte dans le Hainaut, en dessous des sables rapportés par 
Dumont au Systeme Landénien d’un Calcaire grossier avec faune Tertiaire.” Par 
MM. F. L. Cornet et A. Briart. ‘ Bull. Acad, Roy., Belgique,’ 2™° série, vol. xx., 
LANG 
