1915] Andrews: Survey of Lake Butte Des Morts Bog 
199 
so wet that planks had to be laid down to keep one from slipping 
knee deep into the mud. Water oozed up over the planks when- 
ever pressure was applied. A coarse marsh grass covered the 
area. Three feet further out the ground was entirely covered by 
water. Inland the land was hummocky. 
Most of the time — especially in August — the whole marsh was 
completely covered by a thick mat of green algae, which was 
thrown up on the shores by the waves. The shores, the surface 
of the water in the marsh, and indeed the whole lake was a solid, 
Fig. 2. View Looking Northwest Across the Bog. Planks Out- 
line the Small Section Studied. 
opaque green. Some of this matter decomposes, and as the cur- 
rents slowly move along the surface material it shows a wavy and 
streaked appearance. In the latter part of July this coating, or 
scum, became very offensive in its decay. It was composed of 
floating, yellowish masses of more or less spherical outline, some 
of them attaining a diameter of three or four inches. They have 
very little coherence and elude the collector by falling in pieces 
almost at a touch. These masses are composed of Aphanizome- 
non mingled with scattered fronds of Chlorotricha and Anabaena. 
