64 NOTE ON THE CONGLOBATED FOEM OP THE 



of these nodules, when broken open, we find a layer of bivalve 

 shells, and this layer can be traced out of one nodular mass 

 through the intervening laminated marl into an adjoining nodule. 



It seems clearly proved by this occurrence of shells passing in 

 a straight line through these adjoining nodules, and also through 

 the laminated marl which connects them, that the beds in which 

 these nodules now occur was in the first instance composed en- 

 tirely of fine laminated marl, on the surfaces of which when 

 first deposited and laid out on the sea floor, these characteristic 

 moUusca lived, and in which they were eventually entombed. 



These marly beds rest on undisturbed compact beds, and are 

 covered by others equally compact and undisturbed in many 

 places. How, then, has the material, the carbonate of lime, 

 which forms the spheroidal balls been introduced into these beds 

 of pulverulent, dolomitic marl, causing the globular structure. 

 Certainly not from any action or changes taking place beneath 

 the marl, because the stratum underlying the marl has not been 

 in the least disturbed. 



The explanation seems to be that the new substance introduced 

 into these beds of marl has been filtered or dropped in from 

 above ; in fact, that the carbonate of lime was introduced by 

 water surcharged with that material dropping in from the roof 

 of the marl bed, and forming first, on the base of the hard, over- 

 lying stratum, mammillated masses; and lower, in the soft marl, 

 the carbonate of lime continually introduced in drops of water 

 aggregated into spheroidal concretions, the marl itself being 

 either partially incorporated in the concretions or carried ofi by 

 molecular change, caused by the excess of water percolating 

 through the whole series of limestone beds. Though this may 

 not be considered as stalactitic, in the sense in which Prof. 

 Sedgwick explains the form of a stalactite found in an empty 

 cave, yet, as these drops, formed by the percolation of water 

 through the roof of the upper stratum, fall and carry with them 

 carbonate of lime in solution, and as this carbonate of lime is 

 deposited in semiglobose or mammillated, pendent concretions 

 on the roof, and into globular concretions in the bed of loose 

 powdery marl, with more stalagmitic-like forms at the base of 



