166 



BULLETIN OF THE 



Stratified Group. 



The name stratified group is applied to certain rocks whose only 

 common character is that of stratification; and although tho rocks of 

 the Boston basin, and also some of the so-called breccias, arc distinctly 

 stratified, there is no difiSculty in separating the first group, at least 

 geographically, from the others, for its distribution is widely different. 

 The stratified group, consisting chiefly of quartzito and argillaceous 

 rocks, forms an important area, extending from Medford northeast across 

 Spot Pond and Melrose into Saugus. It is a long, narrow band, and 

 fortunately it adjoins the granite, felsite and dioritc, so that we have 

 upon the borders of this area the means of determining the relations 

 of all of the rocks mentioned. The petrological relations of this group 

 and its probable much wider distribution upon tho surface in former 

 times will be considered later. 



Granite. 



The granite occuxjies a large area in Medford southwest of Spot Pond, 

 and also in the eastern part of Melrose, cxtendiug into central and 

 northern Saugus. In Maiden there are four small areas of granite, one 

 near Pleasant Street between Maiden and Medford, another northeast of 

 Prospect Hill, a third along the Newburyport turnpike north of Broad- 

 way station, and a fourth near Franklin Park. 



The relation of the granite to the stratified group is shown by many 

 facts so evident, that, as far as the phenomena themselves are concerned, 

 there is no difference of opinion among observers. 



North of Howard Street, along the Melrose-Saugus line, and at otlier 

 places, the granite occurs in oblong or irregular patches, apparently as 

 an eruptive in the stratified group. The facts in these cases are, how- 

 ever, not as convincing as others so abundant throughout the regions in 

 which the granites predominate. It has been frequently observed that 

 upon Marblehead Neck the coarsely crystalline granite coutains frag- 

 ments of distinctly stratified rocks. In the granite of Medford stratified 

 fragments arc abundant, and sometimes at a considerable distance from 

 the nearest large outcrops of their parent rock. This is especially the 

 case with those found near the western base of Pine Hill. The granite 

 in a beautifully glaciated exposure near the west end of Long Pond, 

 Melrose, envelops several angular pieces of rock in which the stratifi- 

 cation can be readily traced. ' Similar phenomena may be observed upon 



