Luther — Economic Geology ok OnondagU County. 



trary is the case. They are smaller in the lower beds. These cellular lime- 

 stones are the " vermicular limestones " of the older reports. 



In the shaft sunk to the rock salt beds at Livonia, N. Y., at the depth of 

 1,356 feet, thirteen feet above the salt bed, a stratum of this cellular magne- 

 sian limestone was reached, in which the cells were filled with salt. A large 

 block was placed in a running brook, and in a few hours the salt had been 

 dissolved out, leaving the rock in precisely the same condition that it presents 

 when found in loose fragments or in the outcrops in this county. In the 

 beds of limestone lying between the principal gypsum deposits, and more 

 abundantly in that underlying the lower gypsum beds, hopper-shaped mud 

 casts of what are supposed to have been salt crystals, are numerous. They 

 are found in both the cellular and non-cellular layers. 



The "needle cavities," or stylolites, are found in all the limestones, 

 but more abundantly in the more compact layers at the top of the deposit. 

 Gypsum occurs in layers, veins and nodules throughout the entire deposit, 

 but most sparingly in the upper limestones, where it is either anhydrous or 

 in the form of selenite. The two layers of gypseous shales, in which occur 

 the gypsum beds that are quarried, appear, wherever this horizon is exposed, 

 clear across the county, the upper bed forty to sixty-five feet thick, the lower 

 twenty to thirty feet thick; the proportion of clayey matter being much 

 greater at some localities than at others. The upper bed is better in quality, 

 more convenient of access and much thicker. Most of the plaster quarries 

 now operated are in it. It appears to have been deposited in quiet waters, 

 the deposit consisting of gypsum and clayey matter, the sulphate of lime 

 greatly predominating at some horizons, while in others the proportion 

 was small, and a stratum of shale was formed. Where the bed has been 

 exposed for a length of time, it looks like a bank of soft dark shale. The 

 lines of deposition are very even except where water has penetrated to it 

 through a crevice in rocks above and dissolved out the gypsum, leaving a 

 cavern partly filled with the shaly residuum and fallen fragments of the 

 overlying limestones. These caverns or " pockets " are quite common and 

 sometimes extensive. Where the bed of overlying limestones is thin, it is 

 broken through to the surface and "sinks" are formed, thereby increasing 

 the inflowing stream of water and the rate of dissolution. 



In the Heard quarry, a number of these partially filled cavities are 

 exposed, extending from the bottom of the workings to the top, fifty to sixty 

 feet. Many of the minor disturbances of strata in the vicinity of the outcrop 

 of the gypsum beds are doubtless due to dissolution in this manner. 



