4 American Midland Naturalist Monograph No. 6 



northwestern part of Pennsylvania, particularly in the Pymatuning Swamp, 

 between Linesville and Hartstown, in Crawford County. Here, in places, the 

 Sphagnum and Tamarack formerly reigned supreme for acres in extent and 

 the peat deposits are apparently quite deep.* As may be seen in the treat- 

 ment of Sphagnum in this Manual, the Pymatuning Swamp has yielded a 

 goodly share of the species reported for our region. 



The Andreaeales are represented in our region at only one station, although 

 they occur in the mountains both to the south and to the northeast. It is not 

 unlikely that at other stations Andreaea will yet be found to occur in the 

 mountains of central and western Pennsylvania upon sandstone ridges. 



The Bryales include by far the greater number of moss species found in 

 Pennsylvania. Western Pennsylvania as a whole offers quite a variety of 

 habitats and its moss flora is fairly large, although, considering the area cov- 

 ered, there is a noticeable lack of certain species more or less peculiar to high 

 elevations, to outcrops of limestone, and to low-lying marshes and river swamps. 



The northwestern part of Pennsylvania, in a triangular area extending as 

 far south as Beaver County and as far east as Warren County, was worked 

 over by the ice in the Glacial Period and is still in a rather youthful stage of 

 erosion, with a number of small lakes and ponds and considerable areas of 

 poorly drained lands. Occasional Sphagnum bogs occur here as well as 

 swamps along the flood-plains of some of the streams. Such conditions offer 

 suitable habitats for a number of aquatic and swamp-inhabiting species of the 

 Bryales which are not to be found at all or are quite rare in the rest of western 

 Pennsylvania. Presque Isle, near Erie, is a sandspit of about six miles in 

 length and over a mile in width at its outer extremity- and, containing as it 

 does a variety of ponds, lagoons, woodland swamps, marshes, and dry woods, 

 it affords certain habitats which are not duplicated anywhere else in our region. 



The remainder of the region covered by this Manual is thei rath:r charac- 

 teristic hilly country of the Allegheny Plateau, ranging in altitude from about 

 700 feet above the sea, along the flood-plain of the Ohio River, to about 3,200 

 feet above the sea in the mountains of the southeastern part of our region. In 

 the western, southwestern and northeastern parts of our region the general 

 topography is that of an elevated tableland in an active state of erosion, the 

 rocks being largely sandstones and shales, and mainly non-calcareous. There 

 are many steep valleys and precipitous rock exposures with a minimum of 

 swampy areas or ponds. The flood-plains which have developed alona the 

 Ohio River, the Monongahela River, the lower Allegheny River, and the larger 

 tributaries of these streams have been so largely disturbed by the activities 

 of man that they now offer but few opportunities for collection in what must 

 have once been habitats rich in Bryales. 



As the smaller streams in western Pennsylvania are ascended, however, 



* The largest and most interesting part of this swamp has since been cleared and 

 Hooded to form the Pymatuning Reservoir below Linesville and the Wildlife Rufuge above. 



