I20 Swanston— Silurian Rocks of Co. Down. 
represented and in part combined with it, as several of its most characteristic 
fossils have been detected in its highest bands 
The top of the Upper Birkhill Shales, marked by the zone of Rastrites 
maximus , has not yet been detected in Ireland ; did it occur, its peculiar 
group of fossils would at once make it recognisable. Judging, however, from 
the fact that these upper beds thin out as they extend westward from the 
typical Moffat area, and that the zone of R. maximus seems to be absent from 
Wigtonshire, it is not likely that it will be detected here. 
The grits and slates already referred to, which immediately overlie these 
black shales, are similar in lithological character to those of South Scotland. 
There they are the principal rock which forms the mountainous region known 
as the Southern Uplands; in County Down, however, though equally de- 
veloped, their elevation is inconsiderable. As we pass southwards along the 
promontary of the Ards, these rocks assume in places a more flaggy and 
slaty character, and are in the neighbourhood of Greyabbey extensively quar- 
ried and formed into roofing slates. On some of the surfaces exposed at these 
quarries traces of organisms have been detected-tracks of annelids are abundant, 
—but the only forms that admit of identification are Crossopodia Scotica, M‘Coy ; 
Nemertites tenuis , M'Coy; and Nemertites sp. i Still further south, near 
Portaferry, bands of dark slate occur containing a group of Graptolites strik- 
ingly different from any we have yet met with in the district. The paleonto- 
logical break between these and even the highest of the Coalpit Bay zones .s 
almost complete. An examination shows that of the 14 species obtained from 
them, only 3 are common to the two localities, and the n which make their 
appearance for the first time indicate a much higher horizon for the containing 
beds than those in the northern portion of the county. These latter beds have 
no exact paleontological representatives in the typical districts of Scotland 0 
Wales ; their nearest is, perhaps, the rocks of Upper Middle Silurian age known 
as the Gala Group, occurring in the neighbourhood of Galashiels (ij The 
presence, however, of Monographs Riecartonensis and other Upper Sdunan 
species, and the absence of many of the Upper Moffat forms which occurm 
that series in South Scotland, points to a higher place in the Silurian Syste 
than that to which the Gala Group has been assigned. They are mos p 
ably the exact equivalents of the Hawick rocks of Scotland, *ch in erven 
between the Gala beds and the Upper Silurian of Riccarton (2); but as 
(,). Lapworth, on the Lower Silurian Rocks in the neighbourhood of Galashiels. -Trans. 
Edinburgh Geol. Soc., Vol. II., p. 46. 
( 2 ). Lapworth, On Scottish Monograptidae-Geo. Mag., 1876. p. 55 °. 
