en 
172 E, Andrews the Western Boulder Drift. 
visibility of fine lines when observed with a modern microscope 
of high power, since the great angle of aperture of the objec- 
tive permits oblique rays to reach the eye, and Fraunhofer’s 
formula applies only when the eye is perpendicular to the gra- 
ting. Dr. Barnard is therefore of the opinion that the limit 
suggested by Nobert has no real existence. In his letter, 
which I should mention was written before he was aware that I 
Art. X VIII.—On some remarkable relations and characters 
the Western Boulder Drift ; by E. Anprews, M. D. 
tions upon it were obtained at Bloomington, Ill. In sinking 
two coal shafts the workmen first passed through 118 feet of 
unmodified drift clay, whose boulders and pebbles were all of 
northern origin and often scratched by the action of ice. Di 
rectly beneath this was a bed of ancient soil, on which logs of 
