CARBONIFEUOUS DISTRICT OF COLCHESTER AND HANTS. 267 



number of minerals lining or filling veins or fissures. I am inclined 

 to believe, however, that the fibrous gypsum in the gypseous marls 

 has been produced in a different manner from the " combs" of quartz 

 and other minerals found in the fissures of slate, trap, etc. The 

 gypsum veins show no signs of having met in the middle, though 

 they often appear to have been added to at each side ; and we may 

 infer that the prisms of gypsum grew by additions to each end, 

 furnished by water permeating the rock, and pressed the sides of the 

 fissure apart as they grew in length. Veins of fibrous ice are formed 

 in this way in banks of clay, exerting an enormous expansive force, 

 sufficient to break down the strongest retaining walls ; and when 

 circumstances are favourable, these clusters of icy prisms may be seen 

 to raise objects lying on the surface of water-soaked clays to the 

 height of several inches. Wherever segregation and crystallization 

 are going on in the fissures of rocks, similar effects may be produced ; 

 and it is quite possible that they play an important part in geological 

 dynamics. It is at least not unlikely that some of the remarkable 

 contortions and dislocations observed in the gypsiferous rocks of Nova 

 Scotia may have been produced in this way. 



These marly rocks contain a bed of anhydrite and common gypsum, 

 in addition to the gypsum veins above mentioned. 



Proceeding to the southward, along the eastern bank of the river, 

 we reach a high cliff of brownish-red and gray sandstones, dipping S. 

 30° W., and containing a few fossil plants. These beds probably 

 overlie those previously noticed, and much I'esemble the sandstones 

 that in the Joggins section intervene between the lower limestones 

 and the Coal measures. To the southward of this cliff, which is called 

 the Eagle's Nest, the shore for some distance shows no section. On 

 the west side, however, where the rocks corresponding to the Eagle's 

 Nest form a high cliff", they are separated by a fault from an immense 

 mass of gypsum named White's or the Big Plaster Rock, and one of the 

 principal localities of the extensive gypsum trade of this river. The 

 Big Rock at one time presented to the river a snowy front of gypsum, 

 nearly 100 feet in height; but it has been greatly reduced by the 

 operations of the quarrymen, who bring down enormous quantities 

 by blasting. It is a massive bed, arranged in thick layers, and the 

 whole bent into an arched or almost cylindrical form. In its lower 

 part there is much anhydrite, and also dark laminated limestone, 

 having on its surfaces of deposition immense numbers of flattened 

 shells of Conularia. A compact limestone, containing Terebralulce, 

 also appears near the bottom of the mass. Faults, denudation, and 

 disturbance render it quite impossible to discover in the river section 



