There are three ready explanations for dropstones, but all three involve something carrying a stone from somewhere else and dropping it. The first is the mechanism called ice rafting, in which icebergs carrying sediment drift into the open ocean and melt, dropping whatever the ice was carrying. The second involves dead trees being washed out to sea that have stones in their roots. The third explanation is that kelp plants are torn off the seafloor and take stones with them clasped in their holdfasts, which rot and release their stones. Because this rock unit is of Cretaceous age, from a period in which glaciers were scarce or absent on Earth, we can rule out ice rafting.