Lava erupted from fissures into the seawater to form oddly shaped deposits within the sand and mud. All of these features are well exposed on Seboomook Lake, a long narrow lake a few miles northwest of Moosehead Lake. Within the volcanic rocks are distinctive shapes, called pillows by geologists, which form when lava is suddenly cooled by contact with cold water. The process continues as more lava erupts, in this way forming a deposit made up almost entirely of pillows. Figure 5 shows the general character of the outcrop with a very regular succession of continuous beds.
Individual beds range from a few inches to several feet thick.
Most beds are graded. From all of these features, geologists surmise that for each bed the sediment was deposited from a thick slurry of mud and sand that coursed down a submarine slope, dropping the larger sand particles first, then successively finer materials until all the sediment had settled to the bottom. These rocks formed much in the same way that the sandstone formed, except that the slurry of material was mostly mud with little sand. Follow this road to mile 65 where the Seboomook Dam access road intersects it. Alternatively, travelers may come from Rockwood on the west side of Moosehead Lake via the Pittston Farm road.