582 Scientifie Proceedings, Royal Dublin Society. 
about half-a-mile west of Montpelier House, there is a low saddle 
separating a small hill to the north from the rest of the spur. On 
the east side of this miniature col there has been considerable 
erosion, owing probably to the water having continued to pour 
over here until the ice sank to the same level on the outer side of 
the hill. The drainage seems to have been diverted in this way 
before it had time to trench right through the spur, and form a 
gap, such as has been described as occurring on a much larger 
scale on the south of the hill. The amount of erosion in each case 
is roughly proportional to the size of the rock-mass lying to the 
north, and this law seems to hold for all the dry gullies on the 
northern slopes of the Dublin Mountains. 
In the valley in which Montpelier House stands there is a 
considerable deposit, filling up the whole of its bottom. At the 
surface nothing is seen except local hill wash, but several pits 
opened into it have revealed limestone gravel beneath, and it is 
probable that the local wash is only a surface layer overlying 
gravel of this nature. Some portion of this deposit has most 
likely been carried into the valley by the torrent which cut the 
small half-formed gap just mentioned. 
Similar terraces on the spur above Ann Mount are more diffi- 
cult to explain ; their slope indicates a flow south-west, into Glen- 
asmole, over the spur, which, if they are really cut by marginal 
waters, does not agree very well with the general drainage east- 
ward towards the sea indicated elsewhere. A deposit of gravels 
at this place, at about the same level as the mounds at the mouth 
of the Piperstown valley, also indicates a flow in the same direc- 
tion. A fine pit section in the mound shows cross-bedding 
dipping steeply to the south. The stream, however, which carried 
this gravel into the comparatively still water in which it was 
probably deposited may have flowed directly off the ice instead of 
along the margin. 
In conclusion, I wish to express my thanks to Mr. Seymour 
for his assistance in the levelling operations necessary to determine 
the altitude and form of the floor of the pass, and to Mr. Lamp- 
lugh for much valuable assistance and information, and many 
suggestions, without which it would have been impossible for me 
to bring together and perceive the relation of the facts described 
above. 
