442 



one has in its favour tlie negative evidence furnished by the failure 

 of solutions attempted by competent analysts upon other grounds. 



2, On New Species of Marine Diatomacefe from the Firth 

 of Clyde and Loch Fine. By Professor Gregory. Il- 

 lustrated by numerous drawings, and by enlarged figures, 

 all drawn by Dr Greville. 



In two papers, read before this Society, and subsequently pub- 

 lished in the Microscopical Journal, I described and figured a large 

 number of new species of Diatoms, chiefly marine, which I had found 

 in the Glenshira sand. 



This sand was deposited by the Dhu Loch of Glenshira, at a pe- 

 riod geologically recent, when that lake occupied a higher level than 

 it now does, and extended about two miles farther up the valley. 

 That the Dhu Loch at that period, as well as now, communicated 

 with Loch Fine, so that at high tide the salt water flowed into the 

 lakes, while at low water the current, as in a tidal estuary, flowed 

 outwards, is proved by the fact, that the sand then deposited con- 

 tains more marine than fresh-water species. In the deposit now 

 forming in the Dhu Loch marine forms are also abundant. 



But while it was obvious that all the marine forms of the Glen- 

 shira sand had come from Loch Fine, itself a branch of the Firth of 

 Clyde, it was remarkable that the new forms I had described should 

 not have been found in the Clyde by those who had examined its de- 

 posits. There was indeed one form which I had figured, namely 

 Navicula Hennedyi, which 3Ir Kennedy had shortly before observed 

 in the Clyde, but which had not yet been described. Many known 

 forms were also common to the Glenshira sand and to the Clyde. 



Being firmly convinced that the new forms had also, so far at 

 least as they were of marine origin, conic from the Clyde, I resolved 

 to explore such Clyde deposits as I could obtain ; and having pro- 

 cured several, the result has entirely confirmed my anticipations, 

 and has, besides, brought to light a large number of additional un- 

 described forms. 



The materials I have examined are II in number, of which, 3 

 were from Lamlash Bay, one from Corallina ojicinalis, taken from 

 pools on the shore of Arran at Corriegills, and 7 from Loch Fine, 

 four of these having been dixdged by the Duke of Argyll and myself 



