142 proceedings: geological society 



the borders, a little fine sand. This clay, by its character and physio- 

 graphic expression indicates a great system of extinct lakes hitherto 

 undescribed extending from southern Wisconsin to eastern Kentucky. 

 The clay lies at concordant elevations and occupies an aggregate area 

 of several thousand square miles. The physical character, horizontal 

 attitude of the surface, shore features and fossils show that the material 

 is in large part of lacustrine origin, and it appears that the lakes were 

 formed through the rapid development of valley trains on the Mississippi 

 and Ohio in late glacial time the outwash debris damming the lower ends 

 of tributary valleys. The lake deposit is thus a "valley fill," and ranges 

 in thickness up to 130 feet. In each valley the surface of the fill is prac- 

 tically horizontal but the altitude of the surface varies from valley to 

 valley. The height increases regularly from Cairo up the Mississippi 

 and from the same point up the Ohio. The height and hence the extent 

 of the water in each lake being controlled by the river, fluctuated as the 

 river rose and fell, but the lakes served as reservoirs so that the range 

 between high and low water was not so great as it would otherwise have 

 been. Shore features were generally poorly developed but in places, 

 as near Madison ville, Kentucky, there are unmistakable beach ridges. 



Discussion of the Cretaceous and Tertiary floras of Alaska. Arthur 



HOLLICK. 



About 200 separate collections of fossil plants from Alaska were sub- 

 jected to critical examination. The localities represented range from 

 Herendeen Bay near the end of Alaska Peninsula, along the coast line to 

 Prince of Wales Island, and through the interior down the Yukon Valley 

 from Eagle to the vicinity of Kaltag, besides several scattered localities 

 in the Tanana region. 



Three and possibly four, more or less well-defined floral horizons are 

 represented, with a stratigraphic range extending from the lower part 

 of the middle Cretaceous to the upper Eocene — two in Cretaceous and one, 

 or possibly two, in the Tertiary. 



Exact correlation of the floras is difficult for the reason that certain 

 associations of diverse elements occur together in some of the collections 

 which were not known elsewhere in any known, or described, floras. 

 Apparently in Alaska many old types persisted long after they had be- 

 come extinct in other parts of North America and Europe. Cycads of 

 the genera Zamites, Pterophyllum, and Podozamites are found associated 

 with upper Cretaceous and lower Tertiary angiosperms. The logical 

 assumption would seem to be that the older and more primitive types 

 of vegetation, represented by the cycads, had persisted into more recent 

 times, rather than that the highly developed types, represented by the 

 angiosperm genera, had begun far back in the early part of the Cretaceous. 

 It is evident that the Cretaceous and Tertiary floras of Alaska were as 

 distinct from the equivalent Cretaceous and Tertiary floras of the rest 

 of the North American continent as the living floras of the Pacific Coast 

 are from those of the interior. 



The paper was illustrated by a map of Alaska and a chart showing 

 the correlation of the floras. E. S. Bastin, Secretary. 



