THE PLEISTOCENE OR GLACIAL PERIOD 917 



feet, were deposited upon it. The lower part of the interglacial 

 accumulations constitutes the Don formation, and the upper part, 

 the Scarboro formation. Subsequent to the erosion of the latter, 

 thick sheets of bowlder clay and assorted drift of Wisconsin age 

 were deposited upon it. 



The Don formation contains a warm-temperate fauna and flora, 

 and the Scarboro formation a cold-temperate fauna and flora above. 

 Up to 1900, the flora of the warm-temperate stage had yielded 

 38 species of plants, many of which indicate a climate appreciably 

 warmer (3 to 5) than that of Toronto at present. Among these 

 are the pawpaw and the osage orange, which now flourish only in 

 more southerly latitudes. The fauna includes about 40 species of 

 mollusks, some of which are now living in Lake Ontario, some in 

 Lake Erie, while some are not known in the St. Lawrence waters. 



The flora of the Scarboro beds embraces 14 species of plants, 

 and the fauna 78 species of animals, 72 of which are beetles. This 

 assemblage implies a climate of about the type which now prevails 

 in southern Labrador. The arctic fauna and flora which should 

 theoretically have followed this cold-temperate one, heralding the 

 approach of the next ice-sheet, are undiscovered. 



Other interglacial epochs. In other interglacial formations, 

 there is evidence at many points of an ample growth of vegetation, 

 recorded in peat and muck beds, in humus-bearing soils, and in 

 twigs, limbs, trunks, etc., of trees. From these no great number 

 of species has been identified. Recently, bones of horses (more 

 than one species) have been found in the Aftonian interglacial beds 

 in Iowa, 1 along with bones of elephants and mastodons. 



Marine Life 



On the more northerly coasts. During that stage of the Wis- 

 consin glaciation when the eskers of Maine were being formed, 

 and the sea-level stood higher than now relative to the land along 

 that part of the coast, arctic mollusks abounded in the shore-waters 

 and were buried in marine clays formed contemporaneously with 

 the eskers. 2 The species live now in waters that are near the freez- 



1 Calvin, G. S. A., 1908. 



2 Stone, Mon., U. S. Geol. Surv., XXXIV, 1899, pp. 53-54, and Bastin, 

 Rockland, Me. folio, U. S. Geol. Surv. 



