3()0 rilOCEEDINGS : BOSTON SOCIETY NATURAL HISTORY 
quartzite and bedded sandstone inclusions in the Medford diabase, 
and smaller inclusions of quartzite in the rhyolites; these occur in 
localities fully three quarters of a mile from the nearest known 
sedimentaries. ('2) The order of eruption of the volcanics was : — 
first, granite; second, a series of basic rocks, lamprophyric phases 
of the granite, now metamorphosed to hornblende-biotite schists; 
third, felsitic rock showing three phases, the greater part now 
appearing as granophyr, locally porphyritic and grading on the one 
hand into granite porphyry in which the microgranitic ground mass 
disappears, and on the other into rhyolite and rhyolite porphyries. 
The line of contact between this granophyr and the granite of the 
southern area is not well marked, and it is possible that this latter 
granite is contemporaneous with the granophyr. It has not been 
possible to determine whether the rhyolite breccia of the south end 
of the area is contemporaneous with these latter volcanics. (3) 
Without question the metamorphisrn of the older basic masses in 
the granite, and possibly the production of joint systems in the 
granites and felsites, preceded the intrusion of the diabase dikes. 
(4) Since the intrusion of the dikes, some stresses have been 
exerted, as these dikes are also jointed and in places slickensided. 
Glaciation and Topography. 
Durino; the interval from the time of the last intrusion until the 
eginning of Pleistocene glaciation, the rocks must have undergone 
many changes. At the time of the first ice transgression, the area 
was probably covered with a deep residual soil cover, the product 
of disintegration and decay. In a region where glaciation has left in 
situ only a small amount of residual material from rock decomposi¬ 
tion, the extensive disintegration of the Medford diabase dike could 
not fail to attract the attention of even the earlier geologists. We 
find the first most detailed description of this phenomenon in an 
article, published in 1818, by J. F. and S. L. Dana (Ts, p. 201). 
Later, Professor W. O. Crosby refers (’90, p. 236) to the decom¬ 
position of the rock and the probable time of disintegration; Dr. G. 
P. Merrill (’96, p. 349) adopts and enlarges Professor Crosby’s 
views; Professor G. H. Barton also published a paper on the 
subject of “ Bowlders formed in situ ” in which he refers to the 
disintegration of the diabase (’92, p. 405). 
