Source :

The Boyne Valley in the Ice Age, Robert T. Meehan & William P. Warren

Geological Survey of Ireland

The road from Navan to the M3 Motorway was a wide , alluvium floored tributary stream to the  Boyne. Alluvium is sediment deposited by fluvial (river) processes. This channel conducted water towards the Boyne during the last deglaciation and is now flanked by sands and gravels which were deposited at that time. Turning left at Garlow Cross and looking towards Tara it can be seen that the high hill is enveloped by a lower, flat topped ridge which forms the southern flank of the channel we have just crossed. This is actually a moraine which was deposited by ice pushing up against the bedrock of the Hill of Tara. A moraine is a mound or ridge of unsorted and unstratified  glacial debris, deposited commonly at the ice margin.

Follow the sign for Skryne. Taking the road to the right at the fork for Skyrne Hill, some pronounced rounded hillocks separated by channels are present on either side of the road. These hillocks are composed of gravel and were deposited by meltwater during deglaciation. Their form was accentuated by meltwater flowing between them, causing the channels and the associated steep sides to the features. The road rises towards Skyrne Hill with bedrock cropping out at the top of the hill. A short esker ridge can be seen at the base of the hill between here and the Hill of Tara. An esker is a long narrow sinuous ridge of sand and gravel deposited by a subglacial stream and left behind after the ice melted.

Skyrne Hill

Skyrne was an early Christian monastery, and is called after the Shrine of Saint Colmcille’s relics. The 15th century holy well is dedicated to St. Colmcille. The moat or motte of De Pheipo, the first Baron of Skyrne, can be seen from the hill, as well as the castle that replaced it.

Skyrne Hill, composed of shaley Carboniferous limestone, emerges through the flat and well drained glaciofluvial sands and gravels that extend east from the foot of Tara Hill. Glaciofluvial refers to rivers made up of meltwater from glaciers or ice sheets. Sand is  a sediment of particle size between 2 mm and .06 mm. Gravel is a sediment with particle size over 2.0 mm. These gravels comprise the outwash plain which was deposited in front of the ice as it stood between the two hills during deglaciation. The plain is dissected by a number of channels which eventually link up with the channels east of Garlow Cross.

On the northern side of the base of the hill two elongated hummocks are present. These are two beads of an esker which were deposited (earlier than the outwash gravels) under the ice which filled the area between the two hills. It is difficult to see rock outcrop on the top of Skyrne Hill today as much of the area has been landscaped.

Skyrne to Kentstown to Navan

From Skyrne take the road northwards through Skyrne cross roads to Cusackstown  where the road to the left should be followed. Here, at Cusackstown, the road follows the base of a network of meltwater channels. Drive on to the next cross roads and turn right into Kentstown along the northern edge of the Nanny Valley. This deep valley was again cut by meltwaterr during deglaciation and carried much of the Boyne water while the ice sheet stood just north of here. The road from Kentstown back to Navan follows a till plain with Brownstown Hill, which is rock cored, dominating the landscape on the northern side of the road. Till is sediment deposited by or from glacial ice; unsorted and unstratified, and generally tightly packed.