54 



POST-TERTIARY ENTOMOSTRACA. 



Section showing position of shell-bearing clay at Kilchattan 

 Tile-works, Bute. 



a, Boulder clay, h, Laminated clay, e, Sandy mud, with shells, 

 &c. d, Gravelly mould, e, Peaty mould. 



Passing over e and d, it is in the stratum of muddy sand (c) that the shells occur ; 

 and they are more abundant towards the bottom than near the top. 



The prevailing shells of this deposit are Tellina calcarea, Axinmflexuosus, Scrobicularia 

 prismatica, Cyprina Islandica, Mya truncata, and Vtriculus obtusus. Most of these reach 

 a size rather above the average of those met with in the Clyde beds generally. They are 

 all abundant, from the fry up to the adult forms, showing, as regards this deposit, that 

 the conditions for all stages of growth of these various species had been exceedingly 

 favorable. 



The majority of the Mya were found to have both valves preserved, together with 

 remains of their siphons in position within the shells. This sandy material seems to be 

 favorable for the preservation of this portion of the animal tissue. Siphons have been 

 met with in the soft clay of other localities, but rarely. 



A number of the valves of Mya truncata have thick patches of the muddy sand in 

 which they are imbedded indurated on their inner surface so firmly as not to be removed 

 even by boiling water. Similar hard clays are occasionally found in shells taken from 

 other Post-tertiary deposits. These patches generally do not extend over the whole 

 interior of the shell, but are confined to a particular spot. Sometimes we have 

 met with hard nodules of clay which, when broken, disclose a cluster of small shells 

 embedded within, much like the well-known clay nodules enclosing shells or fish-remains 

 in other formations. 



These indurated patches of sand and clay within the shells, and those enclosing 

 shells, as well as the clay-nodules found in many of our brick-clays, that have no apparent 

 organic nucleus, have all, so far as we have examined, a strong calcareous base, while the 

 clays in which they are embedded have none. 



The grey-coloured laminated clay {h) is formed into layers by thin bands of red sand, 

 which are thicker and more distinct as they approach the bottom, where the clay between 

 them is again divided into exceedingly thin layers. Prom three pounds of this laminated 



