75 



tion of a conglomerate ; yet, like the Marblehead Neck rock, 

 it contains an occasional pebble of a different kind of petrosilex. 

 There are also a few scattering crystals of feldspar. Weather- 

 ing or polishing sometimes reveals the schistosity in rocks which 

 appear otherwise to be destitute of it. This is the case in the 

 vicinity of Cliftondale in Saugus. Here we have jagged patches 

 of a bright-red color and somewhat lenticular outlines enclosed 

 in a dark brownish-red base, and arranged with just enough 

 irregularity to suggest the notion that this rock has resulted 

 from the partial breaking up, in situ, of a very finely schistose 

 petrosilex. These ragged layers have themselves a schistose 

 structure, and in addition to them the base includes pebbles of 

 quartzite and petrosilex (fig. 9, pi. 1), which have sharp, well- 

 defined boundaries, showing no signs of deformation, and un- 

 questionably belonging in the same category with the angular 

 pebbles in the schistose petrosilex on Marblehead Neck. There 

 are many small crystals of feldspar in this rock, mainly in the 

 base. A very similar rock occurs on Oliver Street, near Salem 

 Street, in East Maiden (fig. 10)-. In North Saugus, near the 

 Wakefield line, and east of the road leading north from Cen- 

 tral Brook, there are several small areas of a rock which agrees 

 closely with the schistose petrosilex on Marblehead Neck, ap- 

 pearing to differ only in this, that the structure is more reticulated 

 and the base is more porphyritic. The plan of its structure is 

 shown in fig. 8. Many of the dark, often more or less epidotic, 

 irregular, lenticular bands are decidedly schistose ; and unmistak- 

 able pebbles of this rock have been observed in the adjacent 

 breccia. At Dungeon Rock, in Lynn, there is a distinctly 

 stratified rock in which black, compact layers, varying in width 

 from a mere line to an inch or two, alternate with layers which 

 are grayish and crystalline, consisting largely of feldspar crys- 

 tals , with a small amount of a black base similar to the alternat- 

 ing layers, and an occasional grain of quartz. On a preceding 

 page I have expressed a doubt as to the Huronian age of this 

 rock, and this is not removed by a farther examination. It 

 is quite basic, the crystalline layers affording only 63.6 per 



