126 
Lapworth— Graptolites of Co. Down. 
series. This circumstance is very naturally accounted for. The black shale zones 
of the Moffat series die out one by one, from above, as we pass outward to the 
north-west, from the typical Moffat area. From this cause the Rastrites maxi- 
irius is not present in Wigtonshire, and is consequently missing also from the 
Black shales of the northern part of County Down, which are actually the 
south-westerly extension of the Wigtonshire Silurians. Should the black shales 
be detected in the future in the southern districts of the County Down, the 
maximus zone will probably be found occupying its natural position immediately 
below the greywackes. 
The Hartfell shales are as yet less perfectly represented. The Barren 
Mudstones of the Upper Hartfell are seen in Coalpit Bay ; and a striking proof 
of the perfect identity of these beds is afforded by the fact that they exhibit the 
peculiar fossil-bearing seam occasionally visible in the Moffat area. The asso- 
ciation of fossils, their state of preservation, and the mineralogical character of 
the seam, are precisely identical with those of this persistent seam in Scotland. 
The zone at the summit of the Hartfell shales-viz., the zone of Dicellograptus 
anceps (Nich.) has not yet been discovered. Neither has any trace been found 
of the prolific zone of Plemograptus linearis. The typical, or Dicranograptus 
Clingani zone, is indeed the only portion of the Lower Hartfell whose existence 
in these deposits has been fully established. 
The upper, or fossiliferous portion of the Glenkiln shales, is present at 
Ballygrot (Greypoint), and in the section in Coalpit Bay. All its chief charac- 
teristic fossils have been already collected from these localities. 
The fossils of the overlying sheet of Greywackes and flagstones are those 
of the great Greywacke (Gala or Valentian) group of the South of Scotland. 
They point to a comparatively high place in this group. The association is such 
as we might expect in the Hawick Rocks, which lie at the summit of the Middle 
Silurians of the South of Scotland, but which have not hitherto afforded any 
determinable species of Graptolithina. 
The forms common to Ireland and Scotland may be seen on an inspection 
of the table (p. 124), where the range of the Irish species in the typical Scottish 
series is given. ' 
The Irish species of Graptolithina, though generally in a fair state of pre- 
servation, are usually fragmentary ; and the figuring of even the best specimens 
of the various forms would give a very inadequate idea of their charactenstic 
appearance. As they are precisely identical in every respect with the Scotch 
forms, I have thought it best to figure some of the more perfect examples 0 
the forms occurring -in the County Down from my own collection, which has 
