Geograph - photograph every grid square

The photo shows an outcrop of lava, on the foreshore of Ferryden, near a black coloured shed which is reminiscent of the times when commercial fishing was based there. The outcrop of lava and others to the east of it along shore of the River South estuary are the best exposures of the lower part of the Montrose Volcanic Formation. Although the top surface of the lava flow on the foreshore appears to be quite thin, the Montrose Volcanic Formation in this area is estimated to be about 200m thick. The individual lava flows of basaltic andesite, locally known as scurdy stone or scurdie stone, are typically less than 3m in thickness with the bases of the flows having an irregular flinty, chilled zone. The lack of pyroclastic ejecta in the sequence suggests that eruptions from the Montrose Volcanic Centre were essentially quiescent rather than explosive.
With regard to Ferryden, Dr Heddle (1901) noted that “agates thickly studded the stones of which the houses were built” and this is similarly true for other old buildings in Craig parish such as the walled garden of the Manse of Craig in Kirkton of Craig. During the 1960’s, Rev. W M Diack, M.A., of the Manse of Craig, used local agates to decorate the cemented areas between slabs of stone which had, at an earlier time, formed the walls of nearby Rossie Castle. (Rossie Castle was demolished in 1957.) In addition to collecting agates at many localities in Scotland, Dr. Heddle famously collected agates in the neighbourhood of Ferryden, Scurdie Ness and Usan. Beautiful “Ferryden Blue” agates are much prized by collectors but the site of the legendary Blue Hole, where he collected large and wonderfully patterned agates, remains an unsolved mystery.
The rocks in the Ferryden area are of national importance, both as representatives of the lower part of the Lower Devonian and for their value in reconstructing and understanding the environment and evolution of the Montrose Volcanic Centre. Some of the lavas in this area have been analysed as part of a petrochemical study of the Lower Old Red Sandstone lavas. In addition to this, part of the reason why the rocks at Scurdie Ness are included in the Rickle Craig to Scurdie Ness SSSI is to preserve the agate rich environment in which the mysterious origin and formation of agates can be better understood.