188 ^'HK ICP] AUK IN CANADA. 



with the Saxicava saiul, and apparently resting- on the 

 terraces cut out of tlie okler clays. This is the ari-ange- 

 nient which prevails throughout this part of (.'anada. It 

 is modified l)y the greater or less relative thickness (jf the 

 boulder-clay and Leda clay, by the irregular distril)Ution 

 of the overlying sands, aiul by the projection through it 

 of rid<'es of the underlvin<j; rocks. 



The section at Trois I'istoles may l)e represented as 

 follows in descending order: 



1. ^a)i(f and Gravel, capping the terraces cut in the 



previous deposits, aiul forming slight ridges or 

 eskers in some of the lower levels. It contains on 

 the lower terraces a few shells of Leda and T'cUlna. 

 At the bottom of this deposit there are seen in 

 places many large boulders of Laurentian and 

 Lower Sihu'ian rocks, resting on the Leda clay 

 below. 



2. Leda Clan, exposed in the railway cutting and seen 



also in the edge of the second terrace. Thickness 

 one hundred and twenty feet or more. It holds 

 a few large lioulders and shells of Leda ;/faelal{s — 

 the latter uninjured and with the valves united. 



."». Boulder-elaij, or hard gray till, with l)oulders and 

 stones. Seen in a mill-sluice near the bridge, and 

 estimated at twenty feet in thickness at this })lace, 

 though apparently increasing in thickness farther 

 to the westward. 



4. Shales of Hiluro-Cambrian aue, seen in the bottom of 

 the river near the bridge. They are smoothed 

 over, but show no striae, tiiough they have 

 numerous structure lines which nnght readily be 

 mistaken for ice-striae. 



