IS93-] 33 [Upham. 
General Meeting, March 15, 1893. 
Vice-President B. Joy Jeffries in the cliair. Forty-one ])er- 
sons present. 
Prof. 11. C. Ernst described a new pathogenic Bacilhis. 
Tlie following papers were read : — 
DEFLECTED GLACIAL STRIAE IN SOMEKYILLE. 
l'.y WARREN UPHAM. 
BoiiMers and smaller rock fragments held tirndy frozen in the 
bottom of the ice-sheet, and especially the line gravel and snnd 
caught beneath these masses, were ground and rasped as the 
glacial currents carried them onward. Multitudes of blocks and 
great amounts of graved and sand, thus actuig as graving tools 
in the grasp ot: the ice, were worn to the finest powder, and con- 
siderable depths of the bed-rocks were eroded, much being pul- 
verized, while the jointed structure often permitted blocks of large 
and small size to be loosened and swept away in the basal portion 
of the ice. Because of their mutual attrition, like upper and 
nether millstones, many of the drift boulders and pebbles, and 
nearly the entire surface of the underlying rocks, are distinctly 
planed and scratched. These marks, or striae, on the bed-rocks 
are very interesting, because they record the directions of the 
ice motion.^ They are found on all the rock surface of Massa- 
chusetts, when overlying drift is removed, as on the borders of 
quarries and where the rock is exposed in grading streets or 
digging cellars ; but on many portions of the natural rock out- 
crops they have been effaced by the action of the weather. 
During ray recent examination of the area of Somerville, the 
city of my residence, lying next northwest and north of Boston 
and Cambridge, for the purpose of i)reparing a sketch of its 
geology to be published in connection with a history of its tirst 
fifty years which were completed in 1892, numerous localities 
having widely diverse courses of the glacial striae were dis- 
' Descriptions of the various types of glacial striatioii, planation, and embossment, 
with discussion of their methods of origin and of their signiticance as evidence of the 
prevailing ice currents and of deflections during the glacial recession, are given in 
Prof. T. C. Chamberlin's memoir, "The Rock-Scorings of the Great Ice Invasions." 
Seventh annual report, U. S. geol. survey, for 1885-86, p 147-248, illustrated by 
fifty figures in the text, mostly engraved from photographs. 
PROCEEDINGS B.S. S. H. VOL XXVI, 3 JULY, 1893. 
