The great increase in the cost of the work is due principally to the four above de- scribed additions and modifications namely : the extra depth excavated under the main stone dam , the first ex- tension of 110 feet of the main stone dam , the extension of the main stone dam necessitating the removal of the embankment and core wall and lastly the additional ex- cavation necessary for the foundation of the last exten- sion . Some idea of what these changes have necessitated may be gained from the consideration of but two items , that of the amount of earth excavation which will be trebled and that of the amount of masonry which will be increased from 550,000 to about 800,000 cubic yards . The value of the work done to March 1 , 1904 is $ 5,363,000 . This most important of all structures to this great city , upon which its welfare would be almost wholly depend- ent , had to be mantled with all possible safeguards against its destruction . Thus the writer being brought face to face with the one paramount necessity that of the safety of this structure , was left no alternative but to modify the plan .

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recommended that a committee of three engineers be ap- pointed to pass upon a question of so vital and wide- spread importance . The Commissioners after personal investigation agreed in this and appointed a committee of expert engineers consisting of Messrs . J. J. R. Croes , Past President of the American Society of Civil Engineers ; Edwin F. Smith , Chief Engineer of the Schuvlkill Navigation Company and Elnathan Sweet , former Engineer of the State of New York . The committee after making an investiga- tion reported unanimously recommending this extension of the stone dam to the gatehouse .