360 Mr. C. Lapworth on the Geological 



Llandeilo-Glenkiln beds, here suddenly expires, almost upon 

 the threshold of the Caradoc formation. The Dicranograptidse 

 and the allied group of the Leptograptidae have here their 

 point of culmination and extinction. In point of numerical 

 abundance these two families almost divide the palm with the 

 Diplograptidse on several horizons in this formation ; but, un- 

 like the members of that family, not a single example of either 

 seems to have outlived its highest zones. 



Lower Caradoc {Hartfell). — The typical graptolitiferous 

 deposit of this age is undoubtedly the Hartfell shales of the 

 south of Scotland ; and to the physical and palaeontological 

 scale there exhibited the extra- Scottish Graptolite-bearing 

 Bala deposits must in the meantime be referred. 



In the lower division of the Hartfell shales we recognize 

 three successive zones, of which the lowest may be regarded 

 as intermediate in its palscontological characters between the 

 typical Glenkiln and Hartfell groups. To this transitional 

 zone the majority of the forms common to the Glenkiln and 

 Caradoc strata are as yet restricted. The zone has not yet 

 been certainly detected outside the range of the Moffat shales, 

 except perhaps in Girvan, where it is imbedded in strata full 

 of Bala-Caradoc Crustacea. 



The central [Dicranograptus-Glingani) zone of the Lower 

 Hartfell is the most characteristic band, and is recognizable 

 not only in the Moffat region, but also in Wales, Ireland, and 

 Sweden, and it is, I suspect, no great distance below the 

 typical Bala Limestone itself. 



The highest (Pleurograpius-li?iearis) zone is remarkable for 

 the extraordinary number of Leptograptidas which it contains. 

 This little family culminates upon this horizon, members of 

 its dubiously distinct genera Leptograptus } Amphigraptus } and 

 Pleurograptus occurring in crowds. 



The genus Dicranograptus, Hall, is by no means uncom- 

 mon in the Lower Hartfell beds generally ; but it hardly ap- 

 pears to survive into the highest zone, above which it is 

 wholly unknown. The well-known species Dicranograptus 

 ramosus is almost worldwide in its geographical range ; and 

 so, in all probability, is the intimately allied D. Nicholsoni, 

 Hopk. 



The genus DiceUograptus, however, is the most predomi- 

 nant bifid form. Few of its species have a long range within 

 the formation ; and only three, viz. Dicellograptus Forchham- 

 rneri } Gein., D. elegans, Carr., and D. Morrtsi, Hopk., are as 

 yet known outside the limits of the south of Scotland. 



Leptograptus Jlaceidus, Hall, ranges from the Glenkiln into 

 the top of the Lower Hartfell, where it seems to expire with 



