148 OUR LAKES AND THEIR USES. 
and lowered, _ Such excessive evaporation at that season induces 
the presumption, that there was some other cause for the fall in 
i 
n : 
cubic feet of water. But between , 831 and 1850, the lake dried 
up continually, whilst between 1850 and 1869, it fluctuated con- 
siderably. , though during those 38 ears, the rainfall was often 
heavier than that of 1875, Here, therefore, is additional evidence 
that so: dergroun agen: B 1 draining 
: cy 1s at work, supplying anc 
caf lake, and that in some years this agency is more powert ] ~ 
m others. Extended observation may discover that fissures aM 
Springs in the limestone belt, and trap rock that traverse a portion 
ni the basin, may ‘ys a for the fall and rise of the ~ 
a Y an hypothesis, unsupported at present by any @re®”” 
evidence. Here lies this large expanse of vain inert, impure, * 
