342 



MINERALS AND GEOLOGY 



east respectively. The Post-Glacial deposits belong chiefly to 

 series, as first determined by Sir J. W. Dawson of Montreal: a lowe 1 

 deep-sea formation, known as the " Leda Clay;" and a succeeding deposit' 

 apparently a shallow-sea or shore-line accumulation, known as " Saxi- 

 cava Sand." These occur widely within the district, and at various 

 elevations.* On Montreal Mountain, beds of Saxicava sand, for 

 example, form a series of terraces, one of which is at an altitude of 

 nearly 500 feet above the present sea level. Beauport, below Quebec, 

 is another locality at which these deposits are well exposed ; but they 

 occur also, and over large areas, around Murray Bay, as well as on 

 the Lower St. Maurice, and elsewhere. The more recent formations 

 of the district comprise, principally, the bog iron ore and ochres of 

 the St. Maurice and other localities on the north shore of the St. 

 Lawrence ; the great peat-beds of Lanoraye, Lavaltrie, St. Sulpice, 

 <fec., 011 the same side of the river ; and those of Sherrington, Loiig- 

 ueuil, and St. Dominique, with others on the south shore. Most of 

 these peat beds overlie deposits of shell marl. 



THE ANTICOSTI AND MINGAN DISTRICT. 



This division belongs strictly to the palaeozoic area of the upper 

 St. Lawrence, of which it forms a detached, eastern portion. It in- 

 cludes the large island of Anticosti in the St. Lawrence Gulf, and the 

 group of the Mingan Islands on the opposite northern shore, together 

 with a narrow strip of the latter east of the Mingan River. Its 

 strata consist of Upper Cambrian and Lower and Upper Silurian 

 formations. On the Mingan coast and islands, and throughout 

 Anticosti, these strata are practically undisturbed. They dip, at 

 slight inclinations, in regular sequence towards the Gulf. The great 

 line of dislocation, referred to on page 335 as passing from the head 

 of Lake Champlain to the St. Lawrence in the vicinity of Quebec, 

 and from thence eastwards along the river and the Gulf, runs 

 between Anticosti and the .Gaspe coast ; and appears to have produced 



* The leda clay formation is characterised by the presence more especially of the lamelli- 

 branchiate, leda truncata (fig. 211, page 277) ; whilst the characteristic fossils of the higher 

 deposit comprise : saxicava rugosa (fig. 216), mya truncata (fig. 214), and buccinum undatum 

 (226). 



