PROCEEDINGS : BOSTON SOCIETY NATURAL HISTORY. 
subject says: — “The dike occurs in a region of extensive glacia¬ 
tion.That the disintegration and decay into v^^hich the rock has 
fallen is subsequent to the glaciation, and is not an isolated case of 
protection from erosion, as might at first be thought, is shown by 
the presence of glacial striae still traceable over the surface of por¬ 
tions of the decomposed dike and the deposit of till overlying it. 
It is, of course, possible that the decomposition had set in prior to 
the period of glaciation. That the process had not gone on exten¬ 
sively, however, is evident from the fact that the material was still 
sufficiently firm to receive the glacial markings. We are apparently 
safe in assuming that this disintegration and decay, or degeneratioii, 
as I have called the combined process, and which extends to a depth 
of thirty feet, or perhaps fifty feet or more along joint planes, is 
mainly postglacial. That the degeneration has here gone on more 
extensively, than in other dikes of the vicinity is due, as the writer 
believes, to its coarse and somewhat granular structure, and also to 
the character of the alteration which had gone on prior to and 
contemporaneous with degeneration.” (' 96 , p. 858, 359.) Profes¬ 
sor G. H. Barton states: — “In a few cases striae are to be seen 
crossing surfaces of unchanged rock, and also of the decomposed 
rock in immediate contact, in such a manner as to indicate that the 
now completely decomposed rock was unchanged when the striae 
were formed. Tliis would lead to the conclusion that the decom- 
position has taken place during post-glacial time. This view is 
strengthened by the fact that portions of the rock exposed as out¬ 
crops have remained unchanged, while immediately adjacent por¬ 
tions which have been covered by the soil are highly decomposed. 
This last feature indicates that organic action is a strong factor in 
the production of the rock decomposition.” (’ 92 , p. 405.) 
Statement and consideration of criteria .—As already intimated, 
glacial striae are found in a number of localities, particularly at 
the southern end of the diabase dike. A careful examination of 
all the localities shows that for the most part these striae are on rela¬ 
tively fresh rock. Wherever the surface of the rock has been ex- 
])osed to the atmosphere for a long period the striae have generally 
been obliterated, although the alteration zone, as judged by the ej^e, 
in many examples rarely penetrates more than one inch in depth, 
with no evidence of disintes^ration such as is found elsewhere over 
large areas. In one instance, a small lenticular inclusion of quartz 
