992 Dr. O. S. Du R. Preller—Lakes Zurich and. Wallen. 
of both (granting the serpentine to be of igneous origin) took place 
in the course of the same geological epoch, although this has not yet 
been fixed. At all events, the grounds above stated undoubtedly 
warrant the conclusion that, in the characteristic section of the coast 
east of the Lion Rock, Kynance, the granite was intrusive in, and 
is, therefore, somewhat younger than the serpentine; and this may, 
not unreasonably, lead to the conjecture that both are considerably 
younger than the pre-Cambrian hornblende-schist of the district. 
VI.—Nore on tue Lakes or Zurich AND WALLEN. 
By C. S. Du Ricuz Pretusr, M.A., Ph.D., Assoc.M.I.C.E., F.C.S., F.G.S. 
N the course of the summer 1892, I had occasion to visit and 
examine the drainage area of the Lake of Zurich, including 
that of the Wallensee; and this gave rise to some interesting obser- 
vations relating more especially to the origin of those lakes, to the 
_ high degree of purification of their waters by chemical and mechanical 
agency, and to some noteworthy effects of certain geological changes 
in their watersheds. 
Drainage Area of Lake Zurich. 
The figures indicate the altitudes in metres above the sea-level. 
? \ neoracne § erratic blocks 
a neoraire g erratic blocks 
AA river depostt 
retres above sea-level, 
SLO DrelaseZove sea level 
Section Across Limmat Valley at Zurich, roooooth. 
