NATURAL HISTORY SOCIETY OF GLASGOW. 337 



Smith, many observers have interested themselves in the shelly 

 clays, and a rich harvest of facts and observations has been reaped. 

 Many able papers, containing lists of the organisms found in the 

 clay-beds, have been published in the Proceedings of this Society, 

 and those of the Geological Society of Glasgow. I hope I may be 

 allowed to glean over the field that has been so ably worked by 

 previous observers, and to gather after them a few stray facts. 



The shell-beds of the Clyde district may be roughly grouped 

 according to the matrix or material of Avhich they are composed, 

 viz., clay or sand. In the beds where sand predominates, the shells 

 are generally closely packed together, and are often somewhat 

 worn or abraded, while their colours have faded. In the beds 

 formed chiefly of clay, the shells are thinly distributed, and are 

 generally well preserved, even to their colouring. At Dalmuir 

 and at Old Mains the sandy character prevails. At Cartsdyke the 

 molluscs are found in clay, and are encrusted with many kinds 

 of marine organisms. Though in great abundance, the shells are 

 found in the most confused condition possible ; the causes of 

 which led to much discussion amongst those who investigated its 

 abnormal state some years ago. The shells in the clay beds being 

 sparsely scattered, a collection is more difficult to make than from 

 the sandy deposits ; frequent visits are therefore necessary, and 

 after all, unless fortune befriends the collector, his list may long 

 remain incomplete. 



My attention has been for a number of years directed to the 

 Houston clay-field, and the collection exhibited is the result 

 of many visits. These shell-beds are situated about two and a 

 half miles north-west of Paisley, and are more in the centre of the 

 plain, and further away from the boulder hillocks, from which the 

 boulders and stones so frequently found in the laminated clay may 

 have been derived. It is therefore comparatively free from 

 extraneous stones or boulders, and it is only at very rare intervals 

 that they occur, though they do turn up occasionally. I examined 

 one large block^ of stone covered with Balani, and could only 

 account for its presence there by its being lifted from the shore by 

 ice and dropped into the laminated clay. 



The depth of the clay worked at Houston is about 20 feet. The 

 clay crops out at the surface, and 10 feet down is the shell-bed 

 proper; 10 feet under this, or 20 feet from the surface, there is 

 the appearance of another shell-bed, but whether it is as continuous 



