shelly till

glacial rafts

 

 

The location and stratigraphy at Leavad as shown by Crampton and Carruthers (1914)

The sandstone raft is in black on the section, with glacial deposits below.

Leavad (ND 174462)

Significance: a large raft of Lower Cretaceous sandstone probably transported from the Moray Firth covered by and resting on glacial deposits

This intriguing SSSI and the early literature dealing with it has been reviewed in detail by Gordon (1993). Unfortunately, although the original excavations can still be made out, little sediment is visible on the ground today.

By ~1908 a quarry had exposed a large, weathered mass of sandstone filling a channel on the floor of the Little River. Fossils of Neocomian affinities later established that the rock was Lower Cretaceous in age. The presence of dykes of boulder clay suggested that it might be a large glacial raft carried from the Moray Firth.

In 1910 a series of boreholes were sunk to explore the deposit. The findings were remarkable. Firstly, the raft was huge, estimated at 220 m long, 49 m wide and 8 m thick. Secondly, the associated channel fill was thick, a minimum of 24.1 m. Thirdly, a complex sequence of glacial sediments appears to exist here. Below the raft lie masses of shelly till and a lower inland till. Above the raft, may lie another thin layer  of till. This makes Leavad the only known site where the three main till units recognised in this part of Caithness may be present at a single site. Finally, masses of laminated dark green shelly clay were encountered of possible Miocene to late Pliocene age, a find that may be unique in Scotland. The main foraminifera was identified as Truncatulina praecincta.

The site deserves detailed study but this is no easy task. Pitting by JCB may establish the field relations of the upper part of the deposit, down to around 5 m but the proximity of the water table will be a problem. Perhaps the best approach is an expensive one - a new and dense series of boreholes across the deposit.