The Plankton Algae of the Palisades Interstate Park 115 



distribution of desmids is not the antiquity of the lake but the 

 chemical nature of the water. The most striking instance of this is 

 Devil's Lake in southern Wisconsin, lying in a small quartzite area 

 that is surrounded on all sides for many miles by sandstones and 

 limestones. Desmids are an important part of the flora of this lake 

 and its flora is of a true Caledonian type, while all of the other 

 lakes of the surrounding region that lie in limestone basins belong 

 to the Baltic type. The occurrence of desmid lakes in northern 

 Wisconsin is quite irregular, and it is impossible to predict that any 

 given lake lying in this old geological region will contain desmids. 

 The reason for the " spotty " distribution of lakes of the Caledonian 

 type probably lies in the fact that the old rocks are covered by a 

 mantle of glacial drift 25 to 400 feet thick which is quite variable in 

 character. In the portions of Ontario where I have studied the 

 phytoplankton, the Caledonian formation is of uniform occurrence 

 and it is interesting to note that in this region the mantle of glacial 

 drift is very thin, so that large areas of the underlying country rock 

 are exposed. 



The Caledonian plankton association has certain other character- 

 istics besides a predominance of desmids. In their studies of the 

 Scottish lakes both Wesenberg-Lund ('05) and W. & G. S. West 

 ('03, '05) comment upon the small volume of the plankton. This 

 plankton association is also characterized by the small proportion 

 of blue-green algae, both in shallow and deep lakes, while the number . 

 of species of Protococcales found in these lakes is much smaller 

 than that in lakes of the Baltic type. 



Among the lakes of the Palisades Park region certain of them have 

 a flora that is distinctly of the Caledonian type. Little Long Pond 

 is probably the best example of such a formation and among the 

 eulimnetic organisms found in it are several Staurastrum species 

 (Pis. 17-21), Micrasterias (Pis. 14—16) and various filamentous 

 Desmidiaceae (PI. 22). The blue-green algae are very poorly repre- 

 sented, and while colonies of Coelosphaeriuin (PI, 3, Figs. 7-8) and 

 Anabaena (PI. 4, Figs. 4-6) have been observed, Chroococcus 

 limneticus (PI. 3, Fig. i) is the memfcer of the Myxophyceae that 

 occurs in numbers. In the same way the Protococcales are of minor 

 importance, Quadrigula Pfitzeri (PI. 10, Fig. 6) being the only 

 species of importance. Other lakes of the Caledonian type in this 

 region are Upper and Lower Twin, Summit, and Forest Lakes. 



The distribution of the Caledonian type of lakes in the Park region 

 is shown on Map 2, which also shows the relation of these lakes to 

 the geological substratum. All of the lakes of this type, as well as 

 their drainage basins, lie in the Precambrian gneiss while the two 

 lakes that drain from the limestone region do not have a desmid 

 flora. The fact that there are such natural lakes with a lack of 

 blue-green algae and Protococcales in the Park region is of the utmost 

 importance, since such lakes practically never produce blooms that 

 impair their usefulness. Long Pond, Lake Mombasha, and Hessian 

 Lake, all natural lakes situated in the Precambrian gneiss, are appar- 

 ently of the Baltic type. The geological survey upon which this 



