The core wall was found to be resting upon lime stone that in places was completely disintegrated , to the form of loose sand and other por- tions in the process of disintegrating , were more or less hard , the softer part being in such a condition that it could be easily crushed by the hand to the form of sand and would absorb water as freely as would a sponge . The hardest of this stone was full of eroded , open and mud - filled seams , the existence of mud being evidence that these seams had acted as passageways for water . Under date of April 1 , 1903 , Prof. Burr , who had con- curred in the condemnation of the wall , reported to Mayor Low as to the foundation as follows : " It is most fortunate that the core wall has been removed so as to dis- close the actual situation and thus remove what would have been a source of gravest danger to the completed embankment structure as originally planned . " Prof. J. E. Kemp , of Columbia University and Prof. J. J. Stevenson , of New York University , both geologists , were retained to investigate the locality affected . They re- ported that the conditions were deserving of very serious considerations and that in certain locations the material was for nd to be so soft that in their own words it " runs with water like sand . " Under their advice this loose and disintegrated rock has been removed to the depth of 75 feet below the base of the core wall , for it is only at this great depth that a suitable foundation for extending the dam has been found . The removal of this soft rock and the replacing it with masonry has again materially in- creased the cost of the structure .