No. 8.] SPENCER — GEOLOGICAL SKETCHES. 469 



3. The re-excavation of the Duiidas valley, and the recession 

 of the lake were gradual, as the old shore lines are met with at 

 several different heights. The materi.-d of which these old water 

 margins are composed is t!ic dehris of the Hudson River Forma- 

 tion, which occurs on the north side of the lake, together with 

 some boulders and pebbles of Laurentian age, as well as some 

 material from the Niagara formation ; the pebbles of the last 

 beino; more or less ans-ular, while those of the Hudson River 

 formation are generally oval, and contain numerous fossils^ 

 among tlie more common of which are: Stenopora fibrosa \ Lin- 

 gulcE, Leptwna sericea, Strojyhomena deltoidea, S. nitens, Orthis 

 lynx. 0. occidentalism Rhynchonclhr recnrvirosti'a, Atrypa Headi; 

 Modiolopsis modiolaris and several undescribed species, Cyrto- 

 donta Hindi ?, Ctenodonta, Cleidophorus f Avicula demissa, 

 Amhonychia radiata ; Cyrtolites ornatus^ Murchisonia gracilis; 

 Orthoceras crehriseptum, etc. 



During the epoch of the subsidence of the waters of Ontario? 

 the streams emptying by means of the Dundas valley re- 

 excavated the valley, and in the deeper parts carried away all 

 the deposits of the Erie clay, except the lower portion below the 

 lake level. The highest ridge showing the old water margin is 

 just north of Duudas, and has an elevation of more than 300 feet 

 above the present lake level ; this consequently conceals the 

 lower members of the escarpment to within a 100 feet of the 

 summit. Gravels and sands occur also on some of the ridges 

 south of the town, at a height of over 100 feet, and coincide in 

 elevation with Burlington Heights. Again the same shore line 

 is exposed in the western part of Hamilton, extending to Hud- 

 son Street, where it is no longer seen on the surface ; but some 

 distance east it can again be traced, following the same contour 

 lines as those of Burlington Heights, which, as has been stated, 

 are 107 feet above the lake. It consists of alternate strata of 

 sand and of coarse and fine gravel, in some places being cemented 

 into hard rock by infiltrated carbonate of lime. Among these 

 shore deposits there is very little of the dehris of the Niagara 

 formation. 



The high and narrow ridge which constitutes the "Heights" 

 was probably caused" by the currents of the river flowing from 

 the Dundas valley meeting the waves of the lake beating in the 

 opposite direction ; and consequently the coarser materials carried 

 down by the river were deposited along with the boulders, 



