303 



The section ends here, abutting against a dyke of dia- 

 base, the intrusion having flexed the beds, but little altered 

 them. The dyke has a thickness of 40 to 50 feet (12 to 15 

 m.) and on its opposite side is in contact with the McAra's 

 Brook conglomerate, the bedding of which is tilted in 

 the same general direction as that of the Stonehouse forma- 

 tion, but there is no apparent alteration of the rock. 



Devo7iian. 



Knoydart formation. — The strata of this formation 

 lie in the syncline formed by the Silurian rocks. An 

 erosion unconformity separates the formation from the 

 Silurian, since at McAra's brook it rests on the Stonehouse 

 formation and in McAdam brook on the Moydart (Wil- 

 liams). It does not appear in the shore section, probably 

 having been eroded before the deposition of the Mississip- 

 pian conglomerates. The strata consist of hard red shales 

 interbedded with compact fine-grained grey sandstones. 

 Above the bridge over McAra's brook are sandy shales 

 which were formerly considered to be of tufTaceous origin 

 and have been referred to in the literature as the "ash bed','' 

 but the work of Williams has thrown doubt on this view. 

 Several diabase dykes occur in the lower portion and in 

 the higher rocks of the formation there are numerous 

 small geodes lined with clear crystals of quartz. The 

 available evidence indicates a continental origin for the 

 Devonian sediments and it is very probable that they are 

 the deposits of some Devonian river. From the "ash bed" 

 Ami collected fossils which were identified by A. Smith 

 Woodward and Henry Woodward as Pterygotus sp., Onchus 

 murchisoni, Pteraspis cf. crouchii, Psammosteus cf. anglicus, 

 Cephalaspis n. sp., and Iclithyordichnites acadiensis, the 

 last being impressions made by a supposed animal having 

 sharp pointed spines or similar organs. Fletcher (1887) 

 gives the thickness of measured outcrops as 6.36 feet 

 (193 m.). 



Mississippian. 



McAra's Brook formation (Williams). — This formation 

 begins with a red cross-bedded conglomerate composed 

 of angular fragments of the older rocks, in particular 

 some of the quartz geodes from the Devonian. Above 



