WATER-LIME GROUP. 
143 
desired quality, and sometimes it does not; but if the quality were always uniform, and the 
treatment in preparing it the same, there would be as much certainty in the result as in the 
burning of common quicklime. The evil, however, lies in the following circumstances. The 
rocks used as hydraulic cement, along the Erie canal and the lateral canals, hold two distinct 
positions, but both similar in regard to the nature of their ingredients. The lowest position 
is the beds of passage from the shale of the Niagara group, to the limestone above. These 
beds consist of shale, or argillaceous matter with an intermixture of arenaceous and calcareous 
earths. The passage from the shale is gradual, the proportion of the other earths constantly 
increasing : in the upper part the first is in small proportion, and the latter in excess. The 
central beds are those best fitted for hydraulic cement, while the upper are too calcareous, 
and the lower too argillaceous. 
In like manner, the second position of the water lime is at the passage of the argillaceous 
marls and shales of the salt group to the more pure calcareous formations above ; consequent¬ 
ly there is a gradual diminution of shaly, and an increase of calcareous matter, with occasional 
bands of pure shale. Now it is evident that the rock, taken indiscriminately, will produce a 
lime of very variable quality, from the constantly varying composition of the rock. A single 
stratum, indeed, at an interval of a few rods, may often be of a quality and composition very 
different from the same at another : this may happen, too, without any very sensible difference 
in the external appearance. It requires, therefore, the most constant attention in the selection 
of the material, and a due degree of care in the preparation. There will always be, how¬ 
ever, a tendency to excess of argillaceous matter in the cements as they are at present se¬ 
lected ; and this substance ensures their gradual but constant and certain destruction, to the 
injury of the structure in which they are used. 
The quality of the sand used in the preparation of the cement, is another subject of impor¬ 
tance. In one part of the State, what is called sand, differs essentially from the material which 
is known by the same name in another. In many places a pure siliceous sand is not to be 
found, calcareous and argillaceous earths forming a considerable proportion. In other places, 
the sand is purely or principally siliceous. The subject of cements has, however, been placed 
before the public in the Annual Reports, and it would be unnecessary to go into further detail 
in this place. The position which these substances occupy is indicated in the description, 
and the places through which they pass is readily found by reference to the Geological Map. 
