﻿138 SLAVE RIVER. July, 



Sowerby in 1827 ascertained to be Spirifer acuta j 

 and several new Terebratidw, one of them resembling 

 T. resupinata ; associated with them a Cirrus 

 and some crinoidal remains occur. Not far above 

 this cliif, a vitreous reddish-coloured sienite pro- 

 trudes ; and half a mile or so below it, the stream 

 passes between rounded hummocks of granite, one 

 of which forms an island, the water-course evi- 

 dently following the line of dislocation of the 

 strata. The clustered nests of large colonies of the 

 republican swallow (Hirundo fulva) adhere to the 

 ledges of the limestone cliffs, and the bank swallow 

 (Hinmdo riparia) has pierced innumerable holes 

 in the sandy brows. 



A small tributary enters the river from the left, 

 behind an island, lying a short way below the 

 Bute^ and another comes in from the right, beneath 

 which the brown vitreous sienite re-appears, forming 

 a flatly rounded eminence. Within a mile of this 

 pyrogenous rock, another limestone cliif occurs on 

 the left bank, at the commencement of a pathway 

 which leads over prairie-lands, or through spruce- 

 fir woods, marshes, and by small lakes, to the Salt 

 River, to be hereafter noticed. 



A mile and a half below this are the three 

 Rocky Islands {Isles des Pierres), which is per- 

 haps the best locality on the river for studying 

 the connection of the limestone with the pyro- 



