MUSEUM OF COMPAKATIVE ZOOLOGY. 



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the western shore of Trankcr's Pond, Saugus, and Wenunchus Lake, 

 Lynn. A very fine example of sti;aii(ied inclusions within the granite 

 has been pointed out by Mr. Crosby * at Break-heart Hill, Saugus. The 

 best exposures at this locality are not far from forest Street, on the west 

 side of a private road loading from Mr. Artemus Edmond's northward 

 towards Pleasant Lake. The coarse-grained granite makes very clearly 

 defined contacts with the stratified rocks which it envelops, and the 

 fragments in which the stratification is prominent are large and lunner- 

 ous, and the facts so evident that they cannot bo questioned. It is 

 interesting to notice that tJie strike and dip of the planes of stratifica- 

 tion are about the same in all of the enveloped fragments (strike N. 5 

 10° E. Dip 90°). This phenomenon is developed in a very remarkable 

 degree about half-way between Oakland Vale and Long Pond, where the 

 granite is full of elongated fragments whose stratification is nearly verti- 

 cal, and whose strike is approximately N. 40" E. This direction corre- 

 sponds very nearly to a sort of gneissaid arrangement of the minerals in 

 the coarse granite of adjacent localities where the fragments do not occur. 

 Almost all the varieties of rocks which occur in the stratified group are 

 represented by fragments in the granite. The fragments vary in size 

 from an inch to many feet in length, and are generally more highly 

 metamorphosed than the large mass of the group from which they were 

 derived. The (piartzite, although occurring in very wc. marked frag- 

 ments, is not nearly so abundant as the less sihcious varieties. 



It is probable that the position of tlie fragments, in some cases at 

 least, as well as the gneissoid structure found in the same region may 

 indicate the direction of motion in the enveloping mass at the time of 

 its extrusion. The general distribution of the fragments of the strat- 

 ified group, throughout a greater portion of the granites we have exam- 

 ined, forces us to admit, cither that the granites have moved quite a 

 long distance from the present outcropping stratified group, or else 

 that the latter group at the time of the eruption of the granites had a 

 wider distribution. The large dike of diabase at the west base of Pine 

 Hill, Medford, contains quite a number of fragments which closely 

 resemble the quartzite of the stratified group. If thoy are fragments of 

 quartzite from the stratified group, they must have been brought from 

 beneath the. surrounding fclsite, either from the stratified group in place, 

 or an included fragment in the granite. Such facts render it probable 

 tliat before the granites and felsites reached the surface, the stratified 

 group had a much wider distribution than it has at the present time. 



* Contributions to tko Geology of Eastern Jtassacluisetts, p. 39. 



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