76 THE MICHIGAN ACADEMY OF SCIENCE. 



FOKMATION OF PEAT IN DEAD LAKE. 



GEORGE P. BURNS. 



(Abstract.) ' . 



Dead Lake is located about ten miles north of Ann Arbor, and is one 

 of the numerous glacial lakes found in the valley of the Huron River. The 

 lake is three-fourths of a mile long, running east and west, and one-half a 

 mile wide. A contour map shows that the bottom is divided into four 

 basins, two in the northern part seventy and seventy-two feet deep 

 respectively, and two in the southern part whose greatest depth is thirty 

 and thirty-five feet. The higher ridge runs north and south. This ridge 

 is never more than twelve feet below the surface and in one place comes 

 above, forming an island. This divides the basin into an eastern and 

 western half. 



The bottom of the eastern half is much more shallow in general. In 

 one place the greatest depth for several hundred feet is only ten feet. 

 There begins then a sudden dip and within a distance of 200 feet it drops 

 to seventy feet below the surface. Although the lake reaches a depth of 

 seventy feet in this half, the larger part is comparatively shallow. On 

 the other hand, a large part of the western half is under nearly forty feet 

 or more of water. 



The shores are rather steej) in the south and southwest, but quite level 

 on the other sides. 



The eastern half, with the exception of a small "lake" about 400 feet 

 in diameter, is so densely covered with vegetation that only a very few 

 narrow channels are left through which one can force a boat. The clear 

 water in these channels is only about two feet deep. In this are found 

 Nuphar, Brasenia, Utricularia and other water plants. That is, the entire 

 eastern half of Dead Lake is almost entirely filled with peat. 



Plants are not distributed all around the lake in concentric zones as 

 is so often the case. The filling began on the south side, and on this side 

 the arrangement of plant zones is as follows: — 



I. Oak, hickory, on high gravel bank. 

 II. Elm, maple, growing in five (5) to ten (10) feet of solid ])eat. 



III. Tamarack, poison sumach, growing in peat from ten to thirty- 



five feet deep. 



IV. Cassandra and other shrubs bordering the tamaracks. 



V. Sedges, largely Carex filiformis, growing in as high as sixty-five 



feet of very loose peat. 



VI. Nuphar, with Peltandra, Brasenia, and Utricularias, which fill 



up the few remaining channels, 



A glance at the profile map gives a good idea of the condition in the 

 eastern part of the lake at the present time. This profile runs north and 

 south through the two basins. The southern one is com])letely filled ; the 



