46 W. H. WARREN, 
will also be found as to the distances of the quarries from 
the works, method of conveying stone, and cost per ton in 
place, quantity and cost of various materials dredged, etc. 
Sewerage System.—In sewerage construction, the ques- 
tion of excluding rainfall or admitting a certain portion of 
it into the sewers, as in the so-called combined and 
separate systems, the results of experience up to date, 
according to Mr. Rudolph Herring, m. am. Soc. C.E., M. Inst. C.E., 
appear to be as follows :— 
The combined system is preferable : 
Where rain water must be carried underground 
from extensive districts, especially where closely- 
built upon, and where new sewers must be built for 
this purpose. 
Where purification is not required, or is not difficult, 
and where storm water overflows are not objectionable 
in polluting the streams. 
Where a sufficient amount of water or sewerage is 
available for flushing the larger sewers. 
The separate system is preferable : 
Where rain does not require extensive underground 
removal. 
Where an existing system of old sewers which can- 
not be made available for the proper conveyance of 
sewage can yet be used for storm water removal. 
Where purification is expensive, and where storm 
water overflows would become objectionable. 
Where pumping of sewage is too expensive to admit 
the increased flow from interceptors during rain. 
Where it is necessary to built a system of sewers 
for house drainage at the least possible cost and delay, 
and where the underground rain water removal can 
be postponed. 
