536 J. E. Marr — The Wenlock and Ludlow strata — 



The graptolites are those of the zone of Ci/rtograptiis MurcMsoni. 

 Other zones of Crytograptus may occur in the higher parts of the 

 Bruthay Flags, for the graptolites are usually found in good pre- 

 servation near the base of the flags only, where the beds are less 

 cleaved, owing to the protection aflforded by the hard grits of the 

 underlying Browgill Beds. In this lower part of the flags, grapto- 

 lites may usually be found in a state of relief, though at Cross Haw 

 Beck they are flattened. At this locality the shales at one horizon 

 have the bedding planes crowded with Ci/rtograpius MurcMsoni in 

 all stages of growth. Some of the forms included in the above list 

 are probably referable to Monograptvs personatus, Tullb., as more 

 than one species seems to have been included in Nicholson's vomerinus. 



Lower Coldwell Beds. 

 = Zone of Monograptus Nilssoni? 



In the Lake District, the thin deposit of grit which forms the 

 lower division of the Coldwell Beds has not hitherto yielded any 

 fossils, but in the Ingleborough district the flags containing the 

 grai)tolites of the Cyrlogmptns MurcMsoni zone are succeeded by 

 massive grits (Ac. 2. of Prof. Hughes' sections in Geol. Mag. Dec. 

 I. Vol. IV. p. 846). In 1887' I stated that the well-known Mough- 

 ton Whetstones were possibly intersti'atified with the grits, and I 

 find that the geological surveyors^ record two bands of grit below 

 these Whetstones, whilst the " Wharf e grits" of the surveyors (the 

 same beds as those numbered Ac. 2 by Professor Hughes) immedi- 

 ately succeed them. It is true that the surveyors remark that the 

 " Whetstone-bed belongs to the Upper part of the Lower Coniston 

 Flags," but the line appears to be drawn for convenience where the 

 grits become the dominant beds, and the fossils of the Whetstones 

 indicate a difierent horizon to those of the Lower (Brathay) Flags. 

 I have recorded Monograptus dubius, Suess, M. Nilssoni, Barr., and 

 M. uncinotus, Tullb.? from these beds. Of these, the most charac- 

 teristic is M. Nilsttoni, and the zone may be named after it. The 

 " Wharfe grits " are succeeded by beds which are certainly the 

 equivalent of the Upper Coldwell Beds, so these grits with their 

 Whetstone band represent Lower or Middle Coldwell Beds or both. 

 There is no break betwixt them and the Brathay Flags, and this is 

 important, as we shall see, when we discuss the stratigraphical 

 horizon of the Nilssoni-zone. 



Middle Coldwell Beds. 



=:Zone of Phacops ohtusicaudatus. 



The extraordinary persistence of the bedding-plane containing 

 Phacops ohtusicaiidahis amongst these calcareous gritty flags has 

 been elsewhere noted, and it is only necessary here to give a list 

 of the fossils which have been discovered in this subdivision. 

 They are : — 



1 Geol. Mag. Decade III. Vol. IV. p. 37. 



2 Geology of the Couutry around Ingleborough, p. 13. 



