C. I. Gardiner — Pakeo&oic Rochs near Balhriggan. 399 



Amongst these lavas several bands of ashes were found, one of 

 them fairly coarse, but the bulk of them fine in texture. Two 

 intrusions of a somewhat coarse diabase were also noted. 



The dip of the ash beds was, wherever visible, to the S.S.E,, but 

 its angle could not be determined with accuracy. The coarse ash 

 can be seen in a hand-specimen to include fragments of extremely 

 amygdaloidal lava, and the microscope shows that in the finer rocks 

 these originally pumiceous fragments were also entombed. ^ 



Just south of Balbriggan the cliffs are made of Drift, but at the 

 next headland beyond the village igneous rocks are again found ; 

 these are still andesitic, and are covered by fine grey-green ashes, 

 with, on one horizon, a layer of large included fragments of a fine 

 purple ash. 



About 340 feet of brown slates are th6n seen dipping at about 



,, Hisingeri (Carr). 



From this fossil evidence it seems probable that these slates are 

 at the top of the M. gregarius zone of the Middle Birkhill. 



The next graptolitic black slates are about 600 feet above the 

 lowest one noted above, and has yielded obscure species of 

 Monograptus, but 10 feet higher comes a band with M. spinigerus 

 (Nich.) and M. priodon'i (Bronn), while 70 feet above this band 

 is one with M. spinigerus (Nich.), M. Hisingeri (Carr), and 

 M. Galceensis (Lapw.), and 80 feet higher still a band yielding 

 M. Hisingeri? (Carr). These fossils seem to show that the bands 

 which they characterize are in the M. spinigerus zone of the Upper 

 Birkhills. 



A slight change in the direction of the dip is now seen, the beds 

 being still fine grits with layers of black slates at intervals, and. 

 their dip being 35° S.S.E. The next graptolitic layer, 85 feet 

 ^above the last one mentioned, contains a species which appears 

 to be M. Biccartonensis (Lapw.), and the same fossil occurs in two 

 bands a little higher up in the series. 



About 1,200 feet of rock occur above the highest of these three 

 bands, chiefly made of grey grits, with here and there black slates, 

 and then the beds begin to curve up in the opposite direction and 



^ See Geikie's " Ancient Volcanoes of Great Britain," vol. i, p. 244. 



^ All the graptolites mentioned in this paper have been examined for me by 

 Miss Elles, of Newnham College, Cambridge, and my best thanks are due to her for 

 Iher extreme kindness in so doing. 



