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- 

 mus 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 Pleut ograptus 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 characteristic 

 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 of 

 the forms occurring in the County Down from my own collection, which has 



