170 



BULLETIN OF THE 



rock, but also that they hold within thcmsGlves detached fragments of 

 the granite which they penetrate. The small patch of granite northeast 

 of Prospect Hill, Maiden, is penetrated by one of the largest fclsitic 

 dikes of this region. It may be seen in the clitf directly opposite Fanlk- 

 ncr's station. . Along the Newburyport turnpike in Maiden there is a 

 small area of granite to which we have elsewhere * alluded. Mr. Crosby f 

 regards this rock as granitoid potrosilex. We placed it among the gran- 

 ites not only on account of its granitic structure, but from the fact that 

 it is clearly distinct from the adjoining feisite. In a gravel-pit upon the 

 east side of the turnpike, a short distance north from Salem Street, sev- 

 cral junctions of the granite and feisite may be scon. The feisite is in 

 some places slightly banded along the contact, and the lino of junction 

 between the two rocks can be readily traced from the south part of the 

 gravel-pit for a considerable distance over the hills to the eastward. 

 Passing a short distance northward along the turnpike several low clilfs 

 appear upon the left. In the second of these, two well-marked dikes of 

 reddish feisite occur. One of them is about five feet in width, tlie other 

 about twelve feet, and they cut through an almost vertical cliff of the 

 granite twenty-five feet in height. These dikes may be traced at intervals 

 for nearly a quarter of a mile to the northeast. The granitic rock of this 

 area, as well as that northeast of Prospect Hill, is quite different in its 

 general aspect from the granite of the larger areas to the northward ; but, 

 so far as the facts are known, there seems to be no good reason for sup- 

 posing that it is not granite, or that its relation to the feisite is different 

 from that of the other granites. 



The large granitic mass extending from eastern Melrose into central 

 and northern Saugus is bounded upon the south and east and partly upon 

 the west by feisite, so we would expect to find within this area numerous 

 exposures of the two rocks in contact, and thereby determine their rela- 

 tions. Near the eastern end of Long Pond in Saugus there are several 

 distinct dikes of feisite in the same granite which at the west end of the 

 pond, about one fourth of a mile distant, as already mentioned, contains 

 well-marked inclusions of the stratified group. One of the most dis- 

 tinctly marked dikes may be found upon the eastern end of the granite 

 hill north of Essex Street, about a quarter of a mile northwest from the 

 Newburyport turnpike. The strike of the dike is N. 20° E., and it 

 varies, within a distance of sixty feet, from six to ten feet in width. 



The most interesting and instructive exposures of the stratified group, 



* Proo. Bost. vSoc. Is^at. TTIst., A'ol. XX., p. 357. 



'[■ ContributioTis to tlu; Geology of I''asteni Mas.sjiolinsetts, p. 78. 



