60 On the occurrence of Freshwater Shells, 



holahris, H. tridentata, H. Sayii, H.alternata, a.nd R. fuliginosa 

 were collected, at from three to four and a half feet below the 

 surface. 



About a mile ]^south of Collingwood, a shallow cutting for 

 the road, exhibits the arrangement of the beds of sand and gravel, 

 which at the base of the exposure dip southward at an angle of 

 35° and are overlaid to the surface by unconformable horizontal 

 layers. Here, from the surface to a depth of three feet, PlaTi- 

 orbis trivolvis and Helix fuliginosa, H. tridentata and H. thyroi- 

 des f were found. The summit of this rise is 78 feet above the 

 level of the lake, and from its plotted section appears to have 

 been thrown up by the waves when the edge of the lake ran 

 along the base of its northern slope. 



There are a few specimens of Melania conica in the Geological 

 Museum, from a railway cutting in sand near Collingwood. 



The greater part of the town of Owen Sound is built on a 

 loose deposit of gravel and fine sand at the head of a long arm 

 of the Georgian Bay of the same name. The flat formed by this 

 deposit slopes gradually up from the head of the bay towards the 

 falls of the Sydenham River, which has cut its way through it, 

 and is bounded on either side by terraces of Silurian limestone or 

 marl. Fresh water shells were observed in abundance wherever 

 a section of the sand was exposed, and also, in one place, Helix 

 alternata the most abundant land shell on the shores and islands 

 of Lake Huron. 



The following species were collected in different places in the 

 most central part of the town. One of these, on the bank of the 

 river was about nine feet above the level of the lake ; the others 

 appeared to be a little higher. 



1. Limncea umbrosa, 7. Melania conica, 



2. Planorhis campanulatus. 8. Paludina decisa. 



3. " bicarinatus, 9. Valvata sincera. 



4. " parvus, 10. " tricarinata. 



5. Melania acuta, 11. Amnicola porata, 



6. " Niagarensis, 12. Cyclas similis. 



About a mile south from the mouth of the river, or following the 

 upward course of the valley, the road is cut through a slight eleva- 

 tion in this lacustrine deposit and here also fresh water shells were 

 found embedded in the sand, but neither the species nor individuals 



