6C) W. H. Twenhofel — Geologic Bearing of the ■ 



While engaged in the summer of 1909 in studying, in the 

 interest of the Peabody Museum of Yale University, the 

 Ordovician and Silurian strata of Anticosti Island, the writer 

 had his attention frequently attracted to the peat deposits 

 which are forming on nearly all parts of the island's surface. 

 This island is situated in the northern half of the Gulf of 

 St. Lawrence between 49° 4' and 49° 53' north latitude. Its 

 surface consists of a series of flat and poorly drained raised 

 terraces which are backed by sea-cliflPs of relatively recent age. 



The examination covered the entire coastal portions and 

 several parts of the interior, an area with a maximum length 

 of one hundred and forty miles and a maximum width of a 

 little more than thirty-four miles. 



Descriptio?i of the Deposits. 



The Peat. — The peat deposits of this island, said to be the 

 greatest in Canada,* are practically coextensive with the 

 island's surface. Thicknesses vary from two to ten feet, the 

 minimum thicknesses existing on the slopes of the upland 

 areas where the drainage is best and where decay has advanced 

 farther so that more earthy matter is present. The maximum 

 thicknesses and best quality are found on the lowest terrace 

 and flat, or nearly flat, portions of the higher terraces. On 

 many areas the peat is very black, well compressed and of 

 good quality, showing microscopically few traces of the 

 original vegetation. On other areas it is less compact, of a 

 more or less brown color, and much undecayed matter is 

 present. Both varieties often exist in the same bed and 

 woody matter may range from top to bottom. 



On the eastern two-thirds of the south coast for about 

 eighty miles the lowest terrace is two or more miles wide and 

 here the peat reaches its greatest development as a thick 

 deposit, thicknesses of more than ten feet being common. 

 Numerous other areas of from one hundred to more than a 

 thousand acres, where a thickness of about ten feet exists, 

 occur at all altitudes. 



In many places the surface of the peat beds is marked by 

 low ridges and hillocks and in the lower portions of such beds 

 undulations duplicating these appear, but somewhat more 

 gentle in outline. Such are well shown in the vicinity of 

 Chaloiipe Creek, about sixty miles from the east end of the 

 island, where on cross-section a ripple-mark effect is produced. 

 It is believed that the irregularities of the upper surface are 

 produced by differential growth of vegetation, these irregular- 

 ities under compression tending to flatten out. 



Suhstratuon of the Peat Beds. — The substratum on which 

 the peat rests consists of Ordovician and Silurian limestones 

 * Logan, W. E., Eep. of Progress, Can. Geol. Surv., p. 783, 1863. 



