164 Spencer : Geology of the Halifax Hard Bed Coal. 



It will be well to bear in mind this great fact, as it will enable us 

 to comprebend the great change in physical geography which took 

 place before the next layer above it was formed. I'his layer is almost 

 entirely composed of marine shells, belonging chiefly to the genus 

 Aviculo-pecteiij but having associated with it many other genera of 

 marine shells. The Aviculo-pecten bed is about from three to six 

 inches in thickness, and is overlaid by a bed of shale of about three 

 to six feet in thickness, containing a large number of nodular concre- 

 tions, locally called " baum pots." They derive their name of " baum 

 pots " from the peculiar odour which they emit when first opened. 

 They are of all sizes, from that of a child's ball up to a foot or more 

 in diameter, and are composed of carbonate of lime, with a thick 

 coating of pyrites. It requires great force to break them open, and 

 it is attended with some little risk, on account of the hardness and 

 brittleness of pyrites, which fly about in all directions, not paying 

 the least regard to hands, face, or legs of the fortunate or unfortunate 

 (as the case may be) operator. But when the balls are broken open, 

 they are found to contain a large number and variety of marine 

 fossil shells, belonging to the genera Goniatites, Nautilus, Qrtlioceras^ 

 Be.Uerophon^ Bmchmm^ Niicida, Ammlo-pecten^ Posidonia, &c., and also 

 fish remains, sometimes the whole fish admirably preserved. Goniatites, 

 of which there several species, are by far the most numerous fossils, 

 and occur in every stage of growth, from some so minute that it 

 requires the aid of the microscope to discern them, to others several 

 inches in diameter. 



The Nautilus is at once the most beautiful and one of the rarest of 

 fossils. Several species are met with in these balls. The geological 

 pedigree of the Nautilus is one of the most ancient and most con- 

 tinuous of all the most varied forms of life, found in the earth's 

 crust. It is found in the old Silurian rocks, and extends throughout 

 all the succeeding formations, and a few forms still linger on in 

 tropical seas. In this respect there is a great contrast in the history 

 of the Goniatite and the Ammonite, which appear to have delighted in 

 exactly the same conditions of climate as the Nautilus. The Goniatite 

 came into existence in the Devonian era, and swarmed in myriads in 

 the early carboniferous period in this country, and finally, so far as 

 we know, came to an end in the sea in which this marine-bed of ours 

 was deposited. The Ammonite swarmed in countless numbers in the 

 lias and oolite, and finally disappeared towards the close of the chalk 

 period. 



(To he coutinued.) 



