KiLiioE — Siliiricm and Metamorj)/iic Rocks. 



143 



foliated, brought up probably by a vertical thrust which leaves on its 

 north side, with the^quartzite, dark-gray and black mica-schist, pebbly 

 grit, and calcareous beds. 



The quartzite group stretches away north-westward from Ashlem 

 Eay, shown in section, to form almost the entire island. It becomes 

 here and there distinctly micaceous and felspatic, and contains thin 

 seams of mica-schist. It forms Dooega Hill (1530), and cliffs 

 overlooking Keel Bay; Finsheen Hill (698), and Slievemore (2204) 

 on each side of Doogort; and Croaghaun Hill (2192) rising up from 

 the ocean, and overlooking Achill Head at the extreme west. 



The mica-schist underlying the quartzite is to be seen in the 

 Doogort Valley, the uppermost beds being here rendered visible by 

 denudation. Limestone here also marks the divisional zone, and on 

 the east side of Doogort Eay, which occupies the extremity of the 

 valley, the dark-gray, almost black schist contains large, round blocks 

 of granite, forming an excellent representative of the boulder-bed of 

 Donegal, occurring, it will be remembered, as here, below the 

 quartzite group. 



Fig. 7.— Section across Doogort Bay, showing mica-schist {m) over-riding 

 Slievemore quartzite {q), and overlain by Hmestone {Is.), boulder- 

 deposit {b), and quartzite (/). 



The quartzite of Slievemore strikes obliquely toward Doogort Bay 

 on the west side, with nearly vertical dip ; but half a mile south 

 of the village the quartzite joins that on the east side, a fault only, 

 with probably a reverse throw intervening. Here, therefore, we 

 have laid bare, by denudation, another instance of an anticlinal fold, 

 though pushed westward along the thrust plane ; for on the west side 

 of the valley or bay neither the black schist, boulder-deposit, nor 

 limestone band appears. The conditions seem to be as represented 

 in the section here given. The boulder-deposit is represented in 

 conglomeratic beds in Inishgaloon Island, opposite Keel, which are 

 traceable along the coast east and west of Dooagh Bay towards Keem, 

 where we again find the base of the great quartzite group. 



