NATURAL AREAS AND REGIONS 



319 



complexity, about midway between 

 Newfoundland . and Alabama. The 

 rocks now at the surface, show by their 

 structure, that they can have attained 

 their present condition only under the 

 weight of a great mass of superincum- 

 bent material, and as the surface shows 

 steeply dipping and truncated layers, 

 it is evident that erosion cut the mass 

 down towards sea level and almost 

 reached it, for the region was worn down 

 to a peneplain, with elevations surviv- 

 ing, called "monadnocks" from the 

 name of the mountain just over the 

 border in New Hampshire. The chief 

 monadnocks are Mount Wachusett, the 

 Watatics, Mount Grace, Brvish Moun- 

 tain, and Asnebumskit Hill. 



This plain was then raised as a whole, 

 without folding, but by broad warping 

 and tilting; so that in the northwestern 

 part of the state it stood aljout 2000 ft. 

 above the sea. As a result of this uplift 

 the streams cut deep trenches. In the 

 soft sandstone of the Connecticut 

 Valley and the soluble limestones of the 

 Housatonic Valley these trenches were 

 widened into broad valleys, the begin- 

 nings of new transient peneplains. 



Thus erosion has marked out the 

 broad topographic divisions of the 

 State, which are also the broad geologic 

 divisions. These divisions are: 



1. The Cambrian and Ordovician 

 limestone valley of the Housatonic, in 

 which steep schist ridges rise from 

 Greylock to Canaan Mountain. 



2. The broad Archean-Silurian upland 

 of eastern Berkshire County, running 

 through Hoosac Mountain and the 

 "hill towns"— Peru, Washington, and 

 Becket. 



3. The Devonian-Triassic valley of 

 the Connecticut in which there are 

 sharp trap ranges, illustrated by the 

 Mount Tom and Mount Holyoke Ranges. 



4. The central upland, or Worcester 

 County plateau, made up of alternate 

 broad bands of Carboniferous granite 

 and narrower bands of folded schists. 



5. The bordering slope that descends 

 gradually eastward and southeastward 

 from the irregular escarpment bounding 



the central upland. The rocks of this 

 division, which is alumt equal in area 

 to the first four combined, present a 

 greater diversity in kind and structure 

 than those of any other division. The 

 whole complex has been several times 

 folded and faulted and lias been deeply 

 eroded, so that in parts of the area rocks 

 of presumed Archean age are exposed. 

 6. 'J'he Coastal Plain, which includes 

 the Cape Cod peninsula and the islands 

 south of the mainland. 



Soil cover 



Massachusetts is almost wholly cov- 

 ered by Quaternary glacial drift, forming 

 the only mineral soil. In a few places 

 only are there accumulations of pre- 

 glacial soil. The rocks are too hard and 

 the period since the ice-age too short for 

 the addition of much soil from weather- 

 ing in post-glacial times. 



During the Pleistocene Period the 

 country was covered with ice and accu- 

 mulated rock material, perhaps a 

 mile thick. When the ice melted the 

 material was left as a thin veneer; thin 

 because the rock origin was hard. The 

 layer was thicker in valley's. 



The ice cut deep flutings in the hard 

 Holyoke diabase, formed drumlins first 

 in the Connecticut Valley, a second 

 zone about 8 mi. wide that extends 

 north and south across the State, part- 

 ing on Wachusett, a third zone through 

 Groton and Marlboro, and a fourth 

 zone along the coast, and formed bowl- 

 der trains that can be followed from 

 many ledges of rock. Well-defined 

 terminal moraines mark the places 

 where the ice remained stationarj- for 

 some time. 



INIany broad sand areas, some of them 

 underlain by laminated clays, mark the 

 sites of lakes, which were fed by the 

 glacial waters and wholly or partly 

 danmied back by the ice. 



On the elevation of the land and the 

 recession of the waters, the streams 

 began to cut into the Pleistocene de- 

 posits, producing steep scarps and liroad 

 alluvial terraces. These terraces were 

 not forested and were therefore sought 



