876 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



surface of the rock, a distance of thirty-four feet. The first five 

 feet consisted of muck, the original soil of the swamp. Then came 

 four feet of tufa, a hard, stony mass, which extended for a con- 

 siderable distance around the spring. This must have been formed 

 from the spring water itself by the separation of a portion of the 

 c^irbonate of lime, which it originally held in solution. 

 The following are the results of its analysis : 



Carl)onate of lime ^ _.. 87.83 



Carbonate of magnesia ._ 1.76 



Oxide of iron 1.71 



Silica (soluble) 0.16 



Alumina 3.38 



Sand and clay (insoluble) i 2.96 



Sulphate of lime trace. 



Organic matter 1.09 



Water... 0.50 



Not determined 0.61 



100. 



The first four constituents were deposited from the water, while 

 the rest were derived from the soil of the swamp. This layer of 

 tufa is more or less open and parous, with numerous cavities, in 

 some of which small stalactitic masses of nearly pure white car- 

 bonate of lime occurred. Leaves and twigs of trees, nuts, «fcc., 

 were occasionally seen in this bed. 



Below this tufa came a layer, twenty one feet thick, of l)lue 

 clay : then four feet of hard pan ; and finally, at a de])th of thirty- 

 four feet, the limestone rock. 



The work of excavation was greatly embarrassed by the abun- 

 dant flow of water from the spring. Horse power and buckets 

 cleared the pit till a depth of sixteen feet was reached, when it 

 was found necessary to employ a steam-pump of eight-horse 

 power. At a depth of twenty-five feet this was found to be insuf- 

 ficient, and hand pumps were added. The crevice in the lime- 

 stone, tlu-ough which the spring rises, is about twelve inches by 

 five, and seems to be quite vertical, as an iron rod could be pushed 

 down to a depth of fourteen feet. Over this crevice was placed 

 an inverted hopper of w^ood, six feet square at the rim, and five 

 feet high, well fitted to the surftice of the rock around the crevice, 

 and tamped with clay to exclude surface-water and prevent leak- 



