The Drift or Boulder Formation* 327 



200 or 300 feet ; and tlie highlands in Oxford are frequently 100 

 or 200 feet, and even more ; and the banks of the Grand River 

 often expose a yery considerable amount. 



" As to the sources whence the material is derived, the finer 

 parts, considered by themselves, present less evidence than the 

 coarser ; the clay gives no evidence at all. In some portions of 

 the sand, however, magnetic iron ore exists, as on the shore of 

 Lake Ontario at Toronto, where the quantity is so considerable 

 on Gibraltar Point, that if a magnet be thrust into the arena- 

 ceous detritus comprising it, on being withdrawn it will be found 

 covered with small grains of the ore. The origin of this is pro- 

 bably the primary region where magnetic iron ore abounds. 

 The evidence of the gravel and coarser material is more direct. 

 The calcareous pebbles in the country on the south shores of 

 Lake Simcoe are identical with the limestones of Rama, to the 

 north, and their fossil, as well as their minerological character, 

 is an incontestible proof of the source from which they are 

 derived. The testimony of fossils is brought to bear also in the 

 district of country separating Lake Ontario from Lake Erie, and 

 by them it is readily determined that the coarser detritus reposing 

 upon each successive formation, is made up, with the addition of 

 whatever is of primary origin, of material derived from the for- 

 mation itself, or of the ruin of some lower deposit whose outcrop 

 is to the north, or of a mixture of both. The ruins of southern 

 outcrops never repose on northern formations for great distances, 

 and only occasionally for short ones, where the southern outcrop 

 occupying an elevated position in an escarpment, the northern 

 deposit stands at a lower geographical level. Instances of this 

 last condition may be seen on the flank and at the base of the 

 ridge skirting the south side of the lake, where fragments of the 

 Niagara limestones, which constitute its summit, may frequently 

 be found resting on the red marls lower down. But on the con- 

 trary, high up the side of the mountain, in the same range, 110 

 feet above the lake level, often may be encountered the remains 

 of the subjacent blue shales, whose outcrop is buried either 

 beneath the waters of the lake or must be looked for on the 

 opposite shore ; and though the fragments of this individual for- 

 mation may not extend to the margin of Lake Erie, the detritus 

 resting there upon the upper limestones consists chiefly of their 

 own debris, with that of the gypseous series to the north. The 

 great erratic blocks or boulders, when rounded by distant travel, 



