THE GEOLOGIST. 
lyiQN. S. Recent Mnegel (Mytilss edalis) moored by its byssus. 
the means of respiration and the source of food. Tliese live erect 
in the oose, others with plated gills, like the oyster or the spondylus, 
rest on one of their sides, while some like the mussel or the 
terebratula, are moored to the bottom by a byssus or set of natural 
cords. Each, however, has its normal position, and each thus by 
its position in the mud or rock, tells us, more or less distinctly, 
where it died, whether in its native home or at some distant spot. 
We know too by their being disj)osed throughout the sti'atum, 
without regard to special levels, that these molluscs lived and died 
naturally at that very place, that the sediments growing higher and 
higher, — film after film piled over other, — the young fiy settled 
LiGH. G. Shells at all levels in the strata of mud, shewing the gradual accnmulation of sediment 
and the natural interment of the moUuscs. 
above the graves of their progenitors, and like them, in course of 
time were enveloped by the accumulating mud to be again sur- 
mounted by younger colonies who in their turn again succumbed. 
But where all on one line in their normal states, the fossil 
shells make one thin calcareous streak in the consolidated mud. 
