of peat deposits (figure 8-4) which are significant in commercial peat 

 extraction. 



Type 1 (figure 8-4) bogs occur in valleys occupied by streams. The stream 

 flows over peat composed chiefly of decayed marsh and forest plants. One or 

 more heath-covered domes of moss peat may extend along the stream. 

 Groundwater enters the deposit as seepage along the valley walls above the 

 basal clay deposit, and moves toward the stream and down the valley. Type 1 

 bogs may range in size from 30 to 320 acres (12 to 130 ha) and range in thic- 

 kness from 7 to 21 feet (2.1 to 6.4 m) . 



Type 2 (figure 8-4) bogs form in a closed basin. Floating mats of moss peat 

 extend over open water of the vestigial lake or pond. The vegetation cover is 

 scrub/shrub surrounded by tall forest, grading inward to stunted trees and 

 shrubs. Water enters the basin as rainfall or from seepage from basin walls. 

 Most bogs of this type are found in sink holes in the limestone terrain of 

 Aroostook County but several occur in Washington County in large kettle holes. 

 Type 2 bogs are small (5 to 15 acres; 2 to 6 ha) and shallow (<12 ft; <3.8 m) . 



Type 3 (figure 8-4) bogs are plateau-like domes developed on gentle surfaces 

 of sand, gravel, or clay. Surface drainage is diverted around the margins of 

 the bog. Growth of the deposit is maintained by rainfall and groundwater that 

 flows up through the sand and gravel deposit below the bog. The edge of the 

 bog is invaded by trees from the sloping margins. Bogs of this type range 

 widely in size and thickness. An example of this type is Runaway Pond Heath 

 in region 6 (Washington County). Plateau bogs are found only near the coast 

 in regions 5 and 6. 



Type 4 (figure 8-4) are domed bogs that contain ponds arranged in concentric 

 rings. Water gathers in pockets of undulating surfaces in the bog and the 

 ponded depressions are made larger by oxidation of exposed peat. Bogs of this 

 type are generally very large (1000 to 4000 acres; 400 to 1600 ha) and reach 

 depths of up to 25 feet (7.6 m) . The Great Heath in Cherryfield is an example 

 of this type of bog. 



Type 5 (figure 8-4) bogs, the most complex, are those in which domes of moss 

 peat coalesce over divides that separate basins containing peat developed 

 above and below the original pond surfaces. The divides are most likely areas 

 of groundwater exchange between the deposit and the rock. The Meddybemps 

 Heath is an example of this type of bog. 



Peat bog stratigraphy . Cameron (1975) described the general stratigraphy 

 of Maine coastal peat deposits. Physiographic forms reflect the stratigraphy 

 of a peat deposit, and quality factors, especially ash content, reflect the 

 deposit. For purposes of discussion, the deposit may be divided into two 

 parts: (1) the part below the level of the original pond surface and (2) the 

 part above that level. The basal zone (bottom) of Part 1 is clay and peaty 

 clay containing more than 50% ash. Ash content in the overlying clayey peat 

 ranges from >25% to <75%, depending on the pond environment. Algae and pond 

 weeds living in clear water produce peat with low ash content; a clayey peat 

 layer low in ash may have been produced in a pond obliterated by floating mats 

 of marsh and moss vegetation, which continually sink and mix with pond sedi- 

 ments until the surface level of the original pond is reached. 



8-10 



