146 UPPER, OR FLINTY CHALK. 



much disposed to attribute the void spaces in the chalk to a natural con- 

 traction of its substance, as to the disengagement of air. We know that 

 chalk divides, by drying, into compartments that are sometimes very re- 

 gular, nearly in the same way as marl. According to this hypothesis, we 

 may suppose either that the chalk and the flints are of contemporaneous 

 formation, that the elements of flint were mixed with those of the chalk, 

 and that they separated from each other by elective affinity, or that 

 the siHceous matter has been afterwards introduced, and has filled up the 

 cavities left in the chalk." 



Professor Buckland, whose opinions on geological subjects merit the 

 highest consideration, objects altogether to the explanation offered by the 

 Wernerian theory. " It does not," he remarks, " appear possible that 

 the flints could have been formed by infiltration into pre-existing cavities, 

 hke the regularly disseminated geodes of the trap rocks ; since this 

 hypothesis, in the case of chalk, would imply the anomaly of their 

 having once existed uniformly over many hundred square miles, as 

 many strata of air bubbles as there are of flint, alternating with the chalk ; 

 and of which air-holes not one was left empty, or partially filled ; whilst, 

 on the other hand, many of the nodules could not have been formed in 

 such air-holes, as they entirely derive their shape from some extraneous 

 bodies affording a nucleus to the silex that has incrusted them*." He then 

 offers the following ingenious theory, as the result of a diligent investiga- 

 tion of the subject. " Assuming that the mass which is now separated 

 into beds of chalk and flint, was, previously to its consolidation, a com- 

 pound pulpy fluid, and that the organic bodies now enveloped in the 

 strata were lodged in the matter of the rock, before the separation of its 

 calcareous from its siliceous ingredients, he conceives that the bodies thus 

 dispersed throughout the mass, would afford nuclei, to which the flint, in 

 separating from the chalk, would, upon the principle of chemical affinity, 

 have a tendency to attach itself The chalk and flint he considers to 

 have proceeded through a contemporaneous process of consolidation, the 

 separation of the siliceous from the calcareous ingredients, having been 

 modified by attractions, which drew to certain centres the particles of 



* Geological Transactions, Vol. iv, p. 4S.2. 



