No. 3.] SPENCER — PALEOZOIC GEOLOGY. 149 



This last section carries us to a higher horizon th;iij any other 

 mensurnble, yet the highest members of the series is still beyond 

 our reach, being covered by the drift over the gently sloping 

 country. However, if we follow the line of strike westward, and 

 take the levels here, and at the nearest exposures of the Guelph 

 formation, at Gait (which is a few miles north of the line of 

 strike of the Barton Beds) and make allowance for dip, it would 

 approximately be found that the unexposed upper beds of the 

 Niagara formation reach to an additional 80 or 100 feet in 

 thickness. 



According to the reports of the Geological Survey of Ohio, the 

 formation has a thickness of 275 feet in Highland county, and 

 probably 350 feet in the northern part of the State. The Cana- 

 dian Geological Survey estimated the whole thickness at 450 feet 

 in the neighbourhood of Cape Hurd, if the dip were uniform. 



Thus we see that from the western part of New York to Ohio 

 there is no great variation in the thickness of the Niagara depo- 

 sits, where the surface is not removed by erosion, and we may 

 fairly place the accumulations in the Canadian portion of the 

 Niagara sea at 280 feet. 



Not only is the deposition of the whole series literally uniform, 

 but there are certain strata which are recognizable as constant 

 over tlie region under consideration. Of these, the most con- 

 spicuous are the " Chert bed'' (No. 12 of sections), and a thick 

 compact bed of light gray dolomite (varying from four-and-a-half 

 to five-and-a-half feet thick, and numbered 8 in the sections). 

 It was from takinu: the levels of this last bed at xVlbion Falls, 

 Hamilton and Dundas, that I estimated the dip at 25-5 feet in 

 the mile, in direction, about twenty degrees west of south. Loc- 

 ally, however. I found the dip sometimes amounting to 37 feet. 

 The distances of the sides of the triangle formed by the three 

 stations above named, were taken from the large county map. 

 The calculation agreed closely with that made from the approxi- 

 mate height of tlie base of the formation at Limehouse, and that 

 known at Dundas, and taking the direction of the dip to be that 

 found by the above mentioned triangle. 



At Limehouse the surfaces of some of the strata are almost as 

 irregular as those of the Medina at Dundas. On the north side 

 of the Dundas Valley the rocks in some places are almost hori- 

 zontal, but again they are found dipping a few feet in the mile 

 to the northward. This being the case, generally, would make 



