OF WESTERN PENNSYLVANIA. 5 



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 

 the rather characteristic 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 2,800 feet 

 above the sea in the mountains of central Pennsylvania. 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 de- 

 veloped along 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 Bryalcs. 



As the smaller streams in Western Pennsylvania are 

 ascended, however, the valleys often rapidly narrow to a more 

 or less steep rock-walled canon where erosion is highly active. 

 In the narrow valleys the forest coverirg has not been very 

 largely disturbed by man and the damp, cool, shaded habitat 

 with varying substrata of decaying wood, rich loam, shaly soil, 

 bare rock, or living bark, conduces to a rich and varied flora 

 of the Bryalcs. Above this area of active erosion there will 

 usually be found, in the headwaters of the streams, a region 

 which has remained largely unaltered from a former advanced 

 stage of physiographic development and which is characterized 

 by wide valleys with gently sloping soil-covered sides rising 

 to broadly rounded and soil-covered hills. These rounded 

 hills, whose height above the bottoms of the adjacent rounded 

 valleys is rarely more than 300 to 350 feet, are in many places 

 still covered with the native forest consisting mostly of the 

 White Oak. but the moss flora of these forests is poor. 



Good collecting ground for the Bryalcs is also to be 

 found in the mountain^ of the eastern and southeastern parts 

 f the region covered by this Manual, particularly in the steep 

 and rocky gorges which have been cut through the sandstone 

 ridges by the" larger streams. Perhaps the best collecting- 

 ground for the Bryalcs in our whole region is to be found in 

 the vicinity of Ohio Pyle, in Fayette County, where the 

 Youghiogheny River and its larger tributaries have cut out 



