104 PROCEEDINGS: BOSTON SOCIETY NATITRAL HISTORY. 
canic necks which have been flattened out into lenses by lateral pres- 
sure or by tectonic forces, or in the case of the longer masses they 
may have been large dikes. Such relations are, however, improbable, 
and as practically all the areas are lenticular, no matter where inter- 
cepted by the plane of erosion, they may best be called pipes. These 
pipes of intrusive material, it may be supposed, were forced in along 
some plane of weakness subsequent to a period of orogenic disturbance. 
The areas in the northern part of the State have been described as 
batholiths, bosses, sills, and lenses. Of these, the first two should 
have cross-cutting relations with the country rock. This has not been 
definitely shown, and hence their size is the only evidence in favor of 
these forms. The sills and lenses are probably not very different from 
the forms further south. 
Age. 
The schistose structure of the rocks in which the serpentine occurs 
was caused by deformation during the Ordovician period. The ser- 
pentine has not suffered the same amount of metamorphism, and so 
must have been intruded since that time. There is, however, no 
means of telling just how much later they were intruded, but it is 
known that later disturbances of a milder nature occurred, especially 
in the Permian. In some cases the serpentine shows considerable 
shearing which, if not due to expansion during hydration, may be due 
to the forces acting in the Permian. In the case of the serpentines 
of IVIanhattan Island and vicinity (9), which belong to the same belt, 
they can definitely be shown to be older than the Triassic sandstone. 
Thus the age may be said to be post-Ordovician and pre-Mesozoic. 
Linear Distribution. 
The reasons for the very striking linear distribution of the areas of 
serpentine can only be very vaguely stated. The presence of such a 
large body of magma as must be supposed to have existed at one time 
beneath this region, must first be admitted. Then there must have 
been some condition in the overlying rocks that offered less resistance 
to intrusion along this line than elsewhere. Inasmuch as this line 
is parallel to the Green Mountains, as well as to the foliation of the 
