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of North Haven Island, Penobscot Bay, Maine, which are characterized 

 by the same type of pillow structure as the greenstones of Saxony and 

 th6 Lake Superior region. 



"Seen in cross section only, as on a glaciated surface or low cliff on the 

 shore, the rock appears to be divided into irregular ellipsoidal masses or lenses 

 from a few inches to two feet in major diameter. These masses of compact 

 rock are embedded in a matrix which is a schistose phase of the same rock, 

 and the less resistance of the matrix to weathering agencies gives prominence 

 to the structure, the oval sections often being surrounded by narrow crevices." 



Dathe^s hypothesis of contractional parting during consolidation of 

 the flow was considered inapplicable, since it would fail to account for 

 the schistose matrix between the masses. Transition phases between the 

 ellipsoidal rock and the normal diabase with columnar structure were 

 clearly observed, and hence a purely dynamic origin, that of brecciation 

 in situ, was not entirely satisfactory. "In the present case, however, the 

 origin seems to have been compound, a true contraction parting modified 

 by dynamic action." 



"At one locality these structures (columnar and ellipsoidal) can be com- 

 pared with the concentric weathering in a dike, and the contrast is such as to 

 allow no confusion of the three different structures." 



Gregory^^ found among the andesites of the Aroostook area, Maine, 

 "black, rusty-looking, spheroidal and elliptical masses of lava, one to two 

 feet in diameter," strewn over the surface, and solid ledges composed of 

 similar forms whose outlines are well displayed by weathering. The 

 masses are amygdaloidal at the surface and denser within and are ce- 

 mented together by a coarse breccia of glassy material and igneous rock 

 of the same character as the spheroids. Flow into water or watery silt, 

 as supposed for other structures of this kind, may, the author thinks, be 

 the explanation of these; but, on the other hand, they may be "the ropy 

 rolling surface at the front of a lava flow." 



Massachusetts. — Crosby^^ has described the melaphyre flows of Nan- 

 tasket, Massachusetts, in which a compact greenish matrix incloses irreg- 

 ularly rounded amygdaloidal masses from 2 inches to 2 feet in their 

 longest diameters. The amygdules are arranged in concentric lines or 

 ^ones parallel with the exterior, the largest ones being either near the 

 surface or near the center. The surfaces of some of the sheets show 

 rounded multidomical protuberances or swellings from 1 to 4 feet in 



*^ H. E. Gregory: Andesites of the Aroostook volcanic area of Maine. Am. Jour. Sci., 

 4th ser„ vol. viii, 18{)9, pp. 359-369. 



«8W, O. Crosby: Geology of the Boston Basin. Occas. Papers Bost. Soc. Nat. Hist., 

 iv, vol. i, pt 1, 1893, pp. 50-53. 



