part 2] THE YALEJSTIAN SERIES. 155 



into blue shales, and these in turn into green and purple mudstones 

 which contain near their centre the Rastrites-maximics shale-band. 



' These Rastrites-maximus mudstones pass upwards into a group of massive 

 yellow gritstones very similar in their petrological characters to those which 



succeed to the M.-sedgivickii zone About 60 feet of these pale-yellow 



gritstones are here exposed, and form the final member of this . . . Camregan 

 group ' (ojJ. cit. p. 647). 



If the Rastrites-maximus Zone is united with the Upper 

 Valentian, it is impossible not to include with it the rest of the 

 Camregan Group, and accordingly it is here included with the 

 overlying Dailly Stage. There is, moreover, no clear evidence of 

 a close relationship between the lower sandstones of the group and 

 the Monograptus-sedgwicki Shales which adjoin them, as the junc- 

 tion is a fault. On all grounds, however, it is certain that the 

 Camregan Group occupies a higher stratigraphical position than 

 the shales. Further, it will be shown in the sequel that tlie shelly 

 fauna of that group in the Girvan district (and its representatives 

 elsewhere) has many features which unite it with the Upper Yalen- 

 tian and late Silurian rocks rather than with the Lower Valentian. 



It is preferable to modity the existing classification in accordance 

 with recent discoveries rather than abolish it in favour of a new 

 scheme. 



IV. CoMPAEisox or THE Shelly HoRizoisrs or the Girvan 

 SuccEssioiyr with the Graptolitic Scale. 



Newlands Stage. — The Mulloch-Hill Beds occupy the time- 

 interval between the base of the Valentian Series and the horizon 

 of the Glen wells Shales. These shales are comparatively barren ; 

 but Charles Lapworth records Climacograptus scalaris (var. nor- 

 malis f), Dimorphograptus (Diplograptus) acuminatus, and 

 (.^) JSLonograptus tenuis. 



No species of JMonograptus has been recorded in any other area 

 from the same horizon as Diplograptiis acuminatus. If the spe- 

 cimen doubtfully recorded above was a Monograptus, it may have 

 been obtained on a higher level than D. acuminatus ; but, as the 

 total thickness of shales exposed in Glenwells Burn is comparatively 

 small, the occurrence of both species in the same section would in- 

 dicate that the Glenwells Shales represent a horizon at the junction 

 of the two zones, which would enable their position to be fixed very 

 accurately on the graptolitic scale. If this record of 3Ionograptus 

 is erroneous, all that can be stated is that the Glenwells Shales 

 form some part of the D. -acuminatus Zone. That zone appears to 

 extend in the South of Scotland almost, if not quite, to the base 

 of the Valentian, and the great mass of the Mulloch-Hill Sandstone 

 and Conglomerate must represent the lower part of the zone, thus 

 corresponding in point of time to a very small thickness of grapto- 

 litic shales. 



The Newlands Pentavierus Beds. — These are included 

 between the graptolitic shales of Glenwells Burn and those of 

 Q. J. G. S. No. 306. N 



