124 



THE HABITAT OF THE EURYPTERIDA 



in the northern belt of Arenig rocks indicates that the shore was not 

 far distant. There is evidence that during Llandeilo time conditions 

 were less stable in the northern area, for the black graptolite-bearing 

 Glenkiln shales (Upper Llandeilo) often merge laterally into grey- 

 wackes and grits, while sometimes, as for instance in sections at the 

 headwaters of the Girvan River, the Glenkiln fossils occur in "minute 

 dark seams in sandy shales, embedded in massive greywackes and 

 grits" (Peach and Home 215). 



The section which is most complete, showing no disconformities 

 and indicating, therefore, continuous deposition, is that at Moffat- 

 dale about 10 miles to the northeast from Moffat, where in the fa- 



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Fig. io. Columnar Sections of Obdovicic in Moffat District, Scotland 



mous Dobb's Linn anticline studied by Lapworth, the succesions 

 given in the first column, figure io, is shown. It will be seen 

 that the Glenkiln and Hartfell groups (Llandeilan and Carado- 

 cian, respectively), are complete and that the latter is followed by 

 the Birkhill shales (Llandovery) which end with the Rastrites maximus 

 zone (b3), which in turn is conformably followed by the green and grey 

 shales of the Lower Tarannon. Crossing the strike to the northwest 

 for about five miles, the Hartfell section is met with. It is the type 

 locality for the shales of that name. The succeeding Birkhill shales 

 are found to go no higher than the Monograptus gregarius zone (&$), 

 which is conformably followed by the Tarannon grits. The signifi- 



