WATER SUPPLY TO SYDNEY EY GRAVITATION. 105 



The whole face of the country seems to have been completely 

 rooted up by these Crustacea? ; they burrow underground in the 

 swamps in search of food, which they probably obtain from the 

 bulbs of the " lily grasses" just named ; they also abound in all 

 the waterholes. The presence of these animals over this peculiar 

 country may well be regarded as another evidence of the perma- 

 nently swampy character of the land. 



The prevalence of these crayfish or land lobsters should be 

 taken by us as a warning against the risk of making dams within 

 their region of mere earthworks and timber, for they might 

 riddle the strongest structure in a very short time, and perhaps 

 ruin the finest dams that could be thus made. In Victoria many 

 dams have been destroyed by these crayfish, and in America 

 they have the same experience, in support of which I will here 

 quote from the "American Journal of Science and Art" the 

 following applicable passage : — " The habits and instincts of cer- 

 tain crawfishes are very extraordinary ; thus the astaci are migra- 

 tory, and in their travels are capable of doing much damage to 

 dams and embankments. On the little Genesee River they 

 have, within a few years, compelled the owner of a dam to re- 

 build it. The former dam was built after the manner of dykes, 

 i.e., with upright posts supporting sleepers laid inclining up the 

 stream ; on these are laid planks, and the planks were covered 

 with earth. The astaciaus proceeding up the stream w T ould bur- 

 row under the planks, where they rested on the bottom of the 

 stream, removing bushels of dirt and gravel in the course of a 

 night. They travel over the dam in their migrations, often climb- 

 ing posts two feet high to gain the pond above." 



From these remarks, we have further good reason for construct- 

 ing the proposed Loddon dam entirely of cement concrete as one 

 monolith, in the same manner as was adopted by the engineer 

 Herr Ritter, at Frieberg, in Switzerland, as described in my trans- 

 lation from the G-erman of Delebar's paper on the great water- 

 works, for water supply and for extensive motive power, erected 

 there by him so successfully within the last five years from the 

 time of their commencement, and now in full industrial operation. 

 Delebar's paper, with its copies of the Swiss diagrams of the 

 Freiberg works, form an appendix to my first paper on Sydney 

 water supply by gravitation. 



This method of making cement concrete dams has been adopt- 

 ed by Mr. G. Gordon, the Hydraulic Engineer-in-Chief for Vic- 

 toria, who originated w T orks of this nature in India, before he was 

 aware of the somewhat similar system adopted by the French 

 engineers, Messrs. Graeff and Delocre, in their construction of 

 the great Furens dam at St. Etienne. Mr. Gordon has erected 

 a cement concrete dam at Stony Creek, near Geeloncr, and which 



