Coffey and Prakger — The Aiiti im Uaixed Bench. 153 



previously prevailing. Following upon the assumption of a corre- 

 sponding movement at Larne, we shall have the Boulder-clay then 

 dipping below the waves at about the close of the time when the 

 shallow-water clay was laid down at Belfast. On the former land- 

 surface of Boulder-clay, beach-gravels, and in places muds, were laid 

 down. 



The continuance of the depression that allowed the Upper 

 Estuarine Clay to accumulate in, say, five fathoms of water at Belfast, 

 resulted in the formation of up to 12 feet of coarse beach-gravels, the 

 highest beds in the Larne series. It may be pointed out that the 

 same amount of submergence (26 feet below present mean sea-level), 

 which would bring the top of the Larne gravels well within reach of 

 the waves, would provide a depth of 6 fathoms of water over the 

 surface of the Upper Estuarine Clay at Belfast, which is fairly within 

 the depth — 5 to 10 fathoms — for which local geologists have stipulated, 

 on quite other — namely, faunistic — grounds. Subsequently a period of 

 emergence set in. The Larne beds were raised above the sea, where 

 they have remained ever since, and tell us nothing further of fluctua- 

 tions of level ; but the Belfast section continues the story. Over- 

 lying the Upper Estuarine Clay is a bed of clean yellow sand, full of 

 washed single valves of shells derived in part from the upper clay. 

 This shows that the deep-water clay has been raised to near tide-level, 

 allowing the waves to wash over it, and eventually to throw down on 

 it a beach deposit. And, finally, a slight movement of depression 

 may be inferred from the fact that this clean yellow beach has been 

 overlaid once again by muds full of littoral burrowing mollushs. Of 

 this small recent depression of the land there is evidence elsewhere, 

 in the form of peat-bogs now washed by the waves (as at Portrush), 

 and so forth. 



Graph ic Representation of the Changes of Level. 



The series of fluctuations of level a))Ove described may be repre- 

 sented graphically by a diagram such as fig. 1 , Plate Y. Let the vertical 

 coordinate represent vertical distance relative to mean sea-level (the 

 strong horizontal line) ; and let the horizontal coordinate represent 

 geological time. There is a difficulty about the latter, as there are no 

 data wherewith to gauge the period of time represented by each bed. 

 But assuming, to render a diagram possible, a scale of uniform deposition 

 in lieu of a scale of years, we may lay down our Alexandi'a Dock section 

 horizontally across the top of the diagram to a convenient scale. Then 



