1876. 221 [Hyatt. 



greater part of the Neck, the southern shore only and an area to the 

 north, of a few acres, being occupied by the micaceous rocks referred 

 to above. Both these and the porphyrinic rocks are overlaid by patches 

 of coarse granite containing flesh-colored feldspar. The precise deri- 

 vation of the granites could not be determined. When the map was 

 made I supposed them to be volcanic products, and thought they had 

 been derived from the same source as the vein rocks penetrating the 

 Salem syenites. This conclusion, however, is untenable. The Salem 

 syenites, which are so well known from their peculiar lithological 

 characteristics, occupy a space of about fifteen square miles in the 

 townships of Marblehead, Salem, and Swampscot. The whole of this 

 series of rocks has been completely shattered by extensive eruptions 

 from below. This is not only the most remarkable characteristic of 

 the surface, as long since noticed by Professor Hitchcock, but is par- 

 ticularly observable along the cliff exposures of the shore lines ; some 

 of these, where the walls are perpendicular, show the original 

 rocky mass split up into angular fragments from the size of a man's 

 hat to those which are many yards in diameter. The fragments 

 have not been injured by their violent separation, and if the vein- 

 stone could be withdrawn they would fit together with the most per- 

 fect accuracy. The veins are filled with rock, which in some places, 

 is a compact red feldspar, and in others of a syenitic or granitic char- 

 acter, varying greatty in color and aspect. 



The Sftlem syenites are crystalline throughout. There, are, how- 

 ever, indications that they may have been originally stratified de- 

 posits, though this conclusion must at present be considered very 

 doubtful, and is merely mentioned in order to attract attention to this 

 point. It has become evident to me that these Salem syenites are 

 older than the adjacent porphyries and mica slates, and therefore that 

 their veinstones have no relation in point of age' and cannot have 

 been the source from which the somewhat similar overlying gran- 

 ites of Marblehead and Beverly were derived. In fact, so far as my 

 observations go, the conclusion appears to be unavoidable that the 

 Salem syenites are remnants of a much older series of rocks than 

 those to which the porphyries belong. Their characteristics are in 

 every way distinct from the adjoining granites of Beverly, Gloucester, 

 and Peabody, and the veinstones by which they are literally reticu- 

 lated, do not extend upward through any of these or of the interme- 

 diate rocks, the porphyries and the mica schists of Marblehead. 

 These last have been described as Huronian by Dr. Hunt, and so 



