Sir H. H. Hoivorth — The Baltic — The Ancylus Sea. 341 



to shallow rivers and streams, where it occurs on stones and rocks. 

 Jeffreys says he once found it (apparently meaning only once) of 

 a dwarf size in a stagnant pool near Swansea, into which no stream 

 had flowed within the memory of man, in company with A. lacustris. 

 The latter shell is described by him as found on the leaves of water- 

 lilies and other aquatic plants, as well as on fallen leaves of trees, 

 in slow rivers, lakes, canals, marshes, and ponds, from Finland to 

 Algeria. He identifies it with the Patella lacustris of Linneeus. 

 Munthe says his A. fluviatilis is not only a fresh- water but a marine 

 shell, and that he has taken it alive adhering to marine species of algae 

 in the Baltic (G. Jeffreys, op. cit., i, 122, 123). This latter state- 

 ment makes it somewhat inconsequent to name the fresh-water sea 

 of the ^ve-Litorina time from this shell instead of from one of the 

 purely fresh- water forms with which it is associated. 



Munthe points out the remarkable fact that the Ancylus fluviatilis 

 which, he says, characterizes the fresh-water beds we are describing 

 is not found living in the streams of Gotland. It occurs, however, 

 in the brooks of Esthland. The fossil specimens are small and 

 dwarfed, being 3 mm. long and 2 high, compared with the living 

 forms. The largest specimens from the fossil beds elsewhere are 

 5 mm. long, 4 broad, and 3 in height, while the largest living ones 

 from Kuvsjon in Skane are 4 mm. long and 2 high (see Overs. K. V. 

 Ak. F., 1887 and 1888, p. 724). 



These proportions seem to point to the fossil shells in question 

 belonging to Ancylus lacustris rather \h.dkVi fluviatilis, for, as my friend 

 Mr. Sherborn has pointed out to me, the chief distinction between 

 the two shells is that one is much rounder than the other, which is 

 more oval. As they occur in places together it may be that the 

 forms grade into each other, at all events Forbes seems to have 

 treated them as of one species. The matter deserves a more minute 

 analysis at the hands of the Scandinavian geologists. Let us return, 

 however, to the distribution of the fresh-water beds we are discussing. 



The case was carried further when certain clays, not then known 

 to be fossiliferous, which were discriminated by Von Post as far back 

 as 1855, and were called by him ' undrediluviallera,' i.e. lower 

 diluvial clay or lower clay, were identified with the Ancylus beds by 

 Munthe. Von Post described them as found as high as 75 metres 

 above the sea-level, and as consisting of a light grey or blue grey to 

 dark grey bed, with little or no tendency to lamination, and when 

 dry falling apart into fine fragments, and as containing concretions 

 of iron oxide formed round roots from above. 



Erdmann and writers in the Sveriges Geologiska Undersoknings 

 called this clay ' undre akerlera' (underlera), while Munthe, who 

 identified it with the clay of his fresh-water sea, called it Ancylus 

 clay. It has been recognized as existing in Upland, Vestmannland, 

 and Nerike, and probably in various parts of Eastern Sweden 

 (op. cit., p. 263). At Skattmanso, in Western Upland, these Ancylus 

 beds are found of a thickness of 3*55 metres and at a height of 

 36 metres above the sea, and containing a large number of fresh- 

 water diatomaceES, including the now probably extinct Eunotia Clevei, 



