THE SUCCESSION OF DEPOSITS. 53 



Ottawa, are occasionally richly fossiliferous, but more 

 usually are destitute of fossil remains. When dried, the 

 Leda clay becomes of stony hardness, and when burned, 

 it assumes a brick-red colour. When dried and levigated, 

 it nearly always affords some foraminifera and shells of 

 ostracoids; and in this, as well as in its colour and 

 texture, it closely resembles the blue mud now in process of 

 deposition in the deeper parts of the gulf of St. Lawrence. 



The lamination of the Leda clay and its included sand 

 layers, show that it was deposited at intervals, between 

 which intervened spaces when currents carried small 

 quantities of sand over the surface. In these intervals 

 shells as well as sand were w\ashed over the bottom, while 

 ordinarily Leda, Nucula and Astarte burrowed in the clay 

 itself. The layers and patches of stones I attribute to 

 deposit from floating ice, and to the same cause must be 

 attributed the large Laurentian boulders, occasionally 

 though rarely seen imbedded in the clay. 



The material of the Leda clay has been derived mainly 

 from the waste of the lower Silurian shales of the Quebec 

 and Utica groups, which occupy a great space in the basin 

 of the gulf and river St. Lawrence. The driftage of this 

 material has been to the south-west, and in that direction 

 it becomes thinner and finer in texture. The supply of 

 this mud, under the action of the waves, of streams, of 

 the arctic currents and tidal currents, and floating ice, 

 must have been constant, as it now is in the gulf and 

 river St. Lawrence. It would be increased by the melting 

 of the snows in spring and by any oscillations of level, 

 and it is probably in these ways that we should account 

 for the alternations of layers in the deposit. 



Tlie modern deposit in the gulf of St. Lawrence, the 

 chemical characters and coloration of which I explained 



