PENNSYLVANIAN. , 471 



in number. In some places these fine folds have been so compressed and flattened that they 

 constitute the beginning of foUa of a new structure across the old. In one place, also, this 

 rock exhibits the development of a new structure by the rotation in sections of the laminae 

 between fault planes. 



That the phyllite is really uppermost in position with reference to the other rocks of 

 sedimentary origin found in Worcester is shown by its superposition in anticUnes. In deciding 

 as to its position in the geologic series — that is, its age — we rely on the specimens of Lepido- 

 dendron acuminatum iound at the so-called coal mine here in Worcester, and we assign it to the 

 Carboniferous. It probably belongs to an early part of that period. 



On the east this phyllite blends into a rusty, fibroUtic, graphitic mica schist which is found 

 in small, detached patches within the Bolton gneiss area. These are probably remnants, 

 indicating the former greater extension of this schist formation. 



The second and lower formation in Worcester is a micaceous quartzite of a brownish- 

 gray color. This is associated with the phyllite ia the latter's extent across the State and 

 occurs in bands east and west, sometimes also in the niidst, of the phylhte. 



Because of the close relationship which these two formations bear to each other, the 

 micaceous quartzite is also assigned to the Carboniferous period. They have been folded 

 together on a large scale in the Oakdale-Millstone Hill anticHne, the phylUte above and the 

 quartzite beneath, and they have been crumpled together on a small scale in many places, 

 as may be seen in the rocks of the deep cuts of the Boston & Albany and Boston & Maine 

 railroads here in Worcester. These two formations appear, as far as can be seen ia the midst 

 of such severe folding, to be conformable. 



Like the phyllite, the quartzite also shows the development of a new or secondary structure 

 across the old or original structure; and in the case of the rock of Wigwam Hill the new structure 

 was formed by the compression of small folds in the micaceous part of the quartzite, so that 

 these compressed folds have become the folia of the schist as it is at the present time. This 

 quartzite is in a few places conglomeratic, and the pebbles show deformation by pressure, being 

 more or less flattened in the plane of the laminae. 



Penetrating the Carboniferous phylhte and quartzite are granite bosses, of which MiUstone 

 Hill is typical. These granites are later than the Carboniferous. That of Millstone Hill con- 

 tains inclusions of both the phylhte and quartzite. The structure of the adjoining Carbonifer- 

 ous quartzite wraps around this granite, sometimes with the origmal bedding and sometimes 

 across it. The rocks in the immediate vicinity of the granite have been greatly shattered and 

 now frequently appear as breccias or made up of small angular blocks cemented together by 

 fine quartz veins. Even the phylhte included in the granite is brecciated, indicating that the 

 pressure was not excessive when this was included in the molten granite, hence that this granite 

 did not sohdify at a very great depth beneath the surface of the earth. * * * 



The Carboniferous quartzite, traced to the east, blends into a coarser-grained, more highly 

 metamorphosed quartzose mica schist, frequently containing alternating homblendic bands. 

 Between the laminae of this schist there has been forced, by parallel injection, much coarse 

 granite. This schist and granite afford many minerals, both original and secondary, as enu- 

 merated in the study of the quarry near Quinsigamond. The alternation of schist and granite 

 is very gneissoid in appearance and often presents a close resemblance to a metamorphic 

 conglomerate. From this appearance, and from the fact that it extends through the town 

 of Bolton and there contains the well-known limestone mineral locahty, this phase of the 

 Carboniferous quartzite is called the Bolton gneiss. 



It is upon this Bolton gneiss that are spread the patches of the rusty, fibrohtic, graphitic 

 mica schist phase of the Carboniferous phylhte already referred to as indicating the former 

 greater extension of that formation. 



Within this Bolton gneiss are also small areas of crystalline limestone in the towns of Box- 

 boro, Bolton, Northboro, MiUbury, and Webster. These crystaUine limestones aboimd in min- 

 erals formed during the metamorphism, and the Bolton and Boxboro limestones have long 

 been noted for the scapoHte and other minerals they afford. * * * 



