186 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 



taries have been formed in a broad belt of limestone of Cambrian and 

 Ordovician formation. The Taconics are formed of sericite schist. 

 The hills which rise everywhere in the valley, even at times bordering 

 the river, are for the most part portions of the schist and the quartzite 

 formations which through faulting have been separated from the main 

 ranges and are often hard knobs, overlain on their flanks with lime- 

 stone. A narrow band of serpentine is exposed in Florida. 



The greatest differences in soil in the County are due to the presence 

 of limestone in the valleys and its absence from the Plateau and the 

 Tiigher ranges. Another very important factor in the formation of 

 soils of different nature was the glacier. Not only did the glacier 

 transport materials of different composition and mingle them together, 

 not only did it scrape the summits of the hills bare of soil, but at its 

 periods of halt it caused the formation of lakes and streams through 

 whose agency much of the transported and ground material was depos- 

 ited in the form of sand-plains and moraines. On the sides of all the 

 larger valleys are mounds of sandy or gravelly material deposited by 

 the halting ice-sheet, and on many of the valley floors are level sandy 

 plains, the former beds of lakes formed by an ice-obstructed gorge. 



Taking into account the factors of shade, moisture, and soil the 

 ■native plants of Berkshire County may be divided, with more or less 

 exactness, into various groups or associations. The most character- 

 istic of these groups are indicated in the following lists, which are not 

 intended to be exhaustive but merely suggestive. 



(1) Plants growing in water with submersed or floating leaves: 

 Isoetes echinospora, var. Braunii, Sparganiutn angustifolium and S. 



Jluctuans, all the Potamogetons, Elodea, Vallisneria, Ceratophyllum, 

 Nymphozanthus {Nuphar, Man. ed. 7), Casialia, Brasenia, Myrio- 

 phyllum exalhescens and M. verticillatum, var. pedinatum, Bidens 

 Beckii, etc. 



(2) Plants of muddy, sandy or rocky shores : Eriocaulon septangu- 

 ■lare, Eragrostis hypnoides, Carex fiava, var. rectirostra, C. Oederi, var. 

 pumila, Cyperus aristatus, C. esculentus, C. strigosus, Juncus articu- 

 latus, J. hremcaudatus, J. marginatus, J. nodosus, J. pelocarpus, Radi- 



■cida palustris, Hypericum boreale, H. canadense, H. ellipticum, Viola 

 lanceolata, Apocynum cannahinum, etc. 



(3) Plants of low river banks and swales : Pteretis nodulosa {Onoclea 

 ■Struthiopteris), Bromus altissimus, Elymus riparius, E. striatus, 

 Tanicum clandesiinum, Carex crinita, C. cristata, C. grisea, C. lanugi- 



