24 BULLETIN OF THE NEW YORK STATE MUSEUM 



rock a rhombic cleavage. In the third district the gypsum 

 of this horizon does not often occur in layers or veins, it 

 usually occurs in isolated masses of irregular form. At 

 many points there appear to be two ranges or levels of 

 these plaster beds as they are called, separated by shale con- 

 taining hopper-shaped cavities. These cavities are of much 

 interest for they represent the external casts of salt crystals 

 which were probably formed during the evaporation of the 

 water from the basin in which the Salina deposits were laid 

 down. These cavities are from one to ten inches in di- 

 ameter. But few fossils are found in the Salina group, for 

 at the time when the shale and gypsum were deposited the 

 water contained too high a percentage of soluble salts to 

 support animal life. 



The fourth deposit was called the magnesian deposit on 

 account of the assumption that the needle-like cavities were 

 due to the crystallization of sulphate of magnesia. As needle- 

 like crystals of sulphate of lime are well known, and as 

 gypsum is abundant in this horizon, it seems more probable 

 that these needle-like crystals were crystals of gypsum. 



Prof. James Hall* describes the Salina group as follows : 

 Succeeding the Niagara group is an immense development of 

 shales and marls with shaly limestones including veins and 

 beds of gypsum. The general color is ashy approaching drab 

 with some portions of dark bluish green. The lower part is 

 of deep red with spots of green. Succeeding this, where 

 protected from atmospheric influences, the rock is blue like 

 ordinary blue clays, with bands of red or brown. This portion 

 and that succeeding it are often green and spotted, and con- 

 tain seams of fibrous gypsum and small masses of reddish 

 selenite and compact gypsum. From this it becomes grad- 

 ually more gray with a thin stratum of clayey limestone, 

 which is sometimes dark, though generally of the same color 

 as the surrounding mass. The formation terminates upward 

 with a gray or drab limestone called by Vanuxem the 



* Geology of the 4th District. 



