Portlethen Moss millennia of evaporation, further intensifying the soil acidity, fueled by organic matter decaying, with little drainage outlet. A layer of sphagnum moss would have developed at the benthic level of the bog, and additional sphagnum layers floated in mats atop the bog. At an intermediate level of evolution, thick peat layers formed from decay and carbonisation of the rotting sphagnum. Generations of carex and juncus flourished, leading to further decay of these materials and eventual heightening of the organic mass. Finally, secondary vegetation took root in the spongy sphagnum mats adding greater biomass to the bog.In some cases the heavy
Portlethen Moss have been enhanced by proximity to the sea and natural defensive protection of the moss to impede intruders. From Tacitus accounts of the Roman general Agricola, it is known that the Romans were daunted by Portlethen Moss, Netherley Red Moss, Cookney Moss and other local bogs that hindered travel. This is also evidenced by the Roman Camp of Raedykes having been established immediately south of this cluster of mosses; the Romans not being able to progress further north, turned inland toward Netherley.The Portlethen Moss is near the Grampian Mountains. The ancient Causey Mounth passage specifically connected the Bridge of Dee