88 PRINCIPLES OF STRATIGRAPHY 



existed. This period seems to have been characterized by subsi- 

 dence. A period of elevation followed, with an increase in warmth, 

 which reached its maximum when the land stood approximately lo 

 meters higher than at present. This is shown by the boreal mol- 

 luscs Zirphcca crispata and Anomia ephippimn, together with Mytilus 

 cdulis, Tellina baltica, Littorina rudis, and L. palliata, mostly forms 

 now common on the New England coast. With still greater eleva- 

 tion the climate again cooled, until it resembled that of the present 

 time, the maximum elevation being 50 meters above the present sea- 

 level. The first two formations probably were deposited during 

 glacial time, while the succeeding deposits represent post-glacial time. 

 The warm-water fauna has a wide distribution in the arctic, espe- 

 cially recognizable by the shells of Mytilus edulis, and often by 

 Cypriiia islandica and Littorina littorca. Some of the arctic locali- 

 ties where this fauna has been found fossil are the Eranz Josef 

 fjord, East Greenland, Spitzbergen, King Charles Land and Franz 

 Josef Land. It has not yet been found in arctic North America. 



Another fauna, found in parts of the arctic where it is now ex- 

 tinct, and indicating warmer conditions than now, is the Purpura 

 fauna, with P. lapiUus, Pecten islandicus, ZirpJicra crispata, Cy- 

 amiuni minutum and Skenea planorhis. This has been found in 

 northwestern Iceland, in a formation resting in some cases directly 

 upon the peat beds with remains of the arctic birch, Bctiila odorata. 



In North Germany a climate similar to the arctic one is indicated 

 by late glacial or early post-glacial deposits, carrying the molluscs, 

 Vertigo paraccdentata, Succinea scJnimacJicri, Planorhis arcticus, 

 P. stroemi, Sphccrium duplicatiun and Anodonta mutahilis. Arctic 

 conditions in Denmark and Sweden, while the ice still occupied a 

 part of the land, are indicated by deposits containing at the base a 

 fauna with the arctic molluscs, Yoldia arctica, Tellina torelli, and 

 T. loveni, which at present are restricted to seas where the tem- 

 perature in the depths at which the species live scarcely rises above 

 2.5° C. and frequently remains below 0°, even in the warmest 

 months of the year. This corresponded to the time of the Salix 

 polaris flora in Denmark. Higher up, together with a flora in which 

 the birches predominate, occurs Anodonta cygnea, which has been ■ 

 held to indicate a July temperature of 13° to 15° C. Still higher 

 follows the fauna with Zirphcva crispa, Mytilus edulis, Cyprina 

 islandica, etc. 



In northern New England and eastern Canada, the glacial till 

 is followed by the lower Leda clays, the fauna of which {Leda sp., 

 Saxicava rugosa, etc.) indicates a climate like that of southern 

 Labrador. These are followed by the upper Leda clays and sands 



