POST-TERTIARY rOSSILIFEROUS DEPOSITS. 47 



In another, No. 4a, light till, eighteen feet ; yellow clay, five feet. Again, in No. 5a, 

 red till, three feet ; grey till, five feet ; yellow till, four feet. 



In all these bores, some of which extend two hundred feet beyond low water, the same 

 varieties of Boulder Clay have been met with in varying proportions. 



In bore No. 8, sixty yards beyond low water, eighteen feet of sand and shells overlie 

 the red till; but we cannot learn Avhether the shells belong to the glacial or recent 

 period. 



About the same distance beyond low water, No. 12, twenty-seven feet of sand over- 

 lies hght till; another bore, about half-way between this and low water. No. 13, gives 

 twenty feet light till. 



The fossiliferous clay lies in a trough or oblong hollow in the Boulder Clay, crossing 

 the longitudinal section of the dock, and shallowing at both ends. On the south it 

 terminates near the siu'face about two hundred yards west of Garvel Park House, and 

 on the north, at the embankment near the surface, close to the Clyde. 



The length of the trough is about three hundred feet, its breadth twenty-four feet, and 

 its depth, near the middle, fourteen feet. This trough is filled with a remarkable 

 fossiliferous clay, crowded with Post-tertiary Mollusca and other marine organisms, which, 

 like those found in other " Clyde beds," are of arctic type. 



The natural character of this deposit was at first suspected because of (1) the 

 •disorderly manner in Avhich the shells are distributed, and (2) the soft loose state of the 

 clay in which they are embedded, which resembles material that has been roughly drifted 

 rather than regularly deposited. We have come, however, to the conclusion that these 

 shells lived and died where they are now found. 



With regard to the apparent disorder in which they lay, it is well known that where 

 Mollusca congregate, dead shells often preponderate largely over the living ; and that a 

 great number of the shells in this deposit were accumulated as dead shells is evident from 

 the numerous valves having their internal surfaces grown over with marine organisms. 

 Although, on a cursory view, they look as if tossed about, and promiscuously heaped 

 together, yet, on closer examination, this irregular appearance seems to arise chiefly from 

 the presence of so many large valves of dead shells ; and, taking the general arrangement, 

 they alternate very distinctly in layers. 



The loose state of the soft clay may be explained in the following way : 

 This fossiliferous deposit unquestionably rests in a hollow or trough formed 

 in the Boulder Clay. The open shelly clay of the deposit would take in more 

 water from the surface than the stiff compact clay on which it reposes could 

 withdraw, and an excess of water, accordingly, would be retained in the trough. When 

 this was cut through at the deepest part by the excavation of the dock, and the super- 

 fluous moisture to some extent drained ofi", the deposit would naturally be brought much 

 to its existing state. 



Similar cases are by no means uncommon. In uncultivated moorlands, our footing is 



