186 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
taries have been fornuHl in a l)roa<l 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 
higher 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, Sparganiuin an g list i folium and S. 
fluchmns, all the Potamogctons, Elodea, VaUisneria, Ceratophyllum, 
NyviphozaritJms {Nuphar, Man. ed. 7), Castalia, Brasenia, Myrio- 
phyllum cvalbescens and 31. verticillatum, var. pedinatum, Bidens 
Beckii, etc. 
(2) Plants of muddy, sandy or rocky shores: Eriocaulon septangu- 
lare, Eragrostis hypnoides, Carex fiava, var. redirostra, C. Oederi, var. 
pwnila, Cypcrvs aristatus, C. esculentus, C. strigosus, Juncus articu- 
latus, J. brevicaudatvs, J. marginatus, J. nodosus, J. pelocarpus, Radi- 
cula pahistris, Hypericum boreale, H. canadense, H. eUipticum, Viola 
lanccolata, Apocynum cannahinum, etc. 
(3) Plants of low river banks and swales : Pteretis nodulosa {Onodea 
Siruthiopteris), Broimis altissimvs, Elymus riparius, E. striatus, 
I^anicuvi dandestinum, Carex crinita, C. cristata, C. grisea, C. lanugi- 
