/ 



ii2 Swanston — Silurian Rocks of Co. Down. 



another series of mudstones somewhat resembling those noted in paragraph 5 

 of this section. The succeeding rocks in order, still going northward, are a 

 repetition of the mudstones noted in paragraph 5, partially hidden by sand. 

 No rocks are now seen for about 60 feet, and a fault here breaks the continuity 

 of the section, the next beds exposed being — 



7. Black fissile shales and slates dipping S. 20 E. at 75 . These sud- 

 denly curve over to the opposite direction, and a few feet further 

 north regain their original dip. 



The section is again lost for several hundred feet, and the next rock ex- 

 posed is massive grey grits and slates, similar to those on the south side of the 

 bay, and having the normal dip of the rocks of the district. 



Tullygarvan. — This fossil locality is situated about one and a half miles 

 -east of Ballygowan Railway station (Belfast and County Down Railway), in 

 the bed of a small stream which flows eastward through the grounds of Tully- 

 garvan House. The rocks near to the shaft which was sunk in search for coals 

 are of a black carbonaceous character, greatly contorted, and much stained with 

 iron. No fossils have yet been detected in them ; but judging from the few 

 traces obtained from the debris of the sinking, and from the character of their 

 associated mud-stones, they seem to conespond with those in the axis of the 

 anticlinal at Coalpit Bay. Black-slates are exposed further up the stream in 

 several places, yielding in all seven species of Graptolites, referable to the beds 

 described in paragraph 3 of the same locality ; thus pointing to the probability 

 that the rocks here shewn are the westerly extension of those beds. 



Orlock Point.— On the shore to the north-east of the coastguard station, 

 black and red shales are exposed between tide marks for about 200 yards. 

 They are bounded on the north and south by purple slates, dipping S. 20 E. at 

 angles varying from 40 to vertical. It is impossible, however, to arrive at the 

 order of occurrence of the black and red shales here exposed, as they are much 

 disturbed by minor faults cutting through them in various directions. The con- 

 tinuity of the section is also broken by a dyke of fine grained Elvanite 10 feet 

 wide, running from west to east, almost in the direction of the strike of the 

 rocks. This dyke undoubtedly occupies the line of a more important fault as 

 we find the rocks on the south side of it consist of black flinty shales, while to 

 the north these are replaced by brown and purple arenaceous beds which pass 



