142 
GEOLOGY OF THE FOURTH DISTRICT. 
The illustration represents a small portion of the stone as it appears, one part presenting 
the cavities while at the other extremity the crystals still remain. 
In some parts of the salt group, cavities of this kind abound, but I have never seen them 
filled with any crystalline substance. These are probably due to a similar cause, viz. the 
solution and removal of some crystalline matter by atmospheric agency. 
The fossils of this group (except No. 1,) occur at Maffit’s quarry as before stated. They 
are not however well preserved, though their forms are easily recognized. These are all 
figured by Mr. Vanuxem in the Report of the Third District. 
58 . 
1. Orthis? (Delthyris) plicatus. 3. Tentaeulites ornatna 
2. Avieula rugosa. 4. Littorina antiqaa. 
5. Atrypa sulcata. 
6. Cytherina alta. 
Water lime, or Hydraulic cement. 
The subject of water lime as a cement in situations exposed to moisture, or to alternations 
of wet and dry conditions, is one of the highest interest to the people of the State of New- 
York. The great extent of our canals, where this substance is largely used in locks, aque¬ 
ducts, culverts, etc., renders it desirable that the utmost precaution be taken to provide a 
material which shall meet all the requisitions. Since, however, it is acknowledged that much 
of the cement is of inferior quality, and as the subject is especially taken under the direction 
of the engineers to guard against the use of improper materials, it is plain that there is room 
for improvement in this product, either in the article selected, or in the manner of preparing it. 
In order to produce a cement of the desired quality, the admixture of certain ingredients in 
the proper proportions is required. The material selected and used sometimes produces this 
