948 A. W. GRABAU THE TULLY LIMESTONE 



complete, and themselves added very little to the suhstance of the rock. 

 "Recognizable fragments of organisms are wanting; only perfect forms 

 occnr embedded in a fine lime mnd. It is obvious, then, that the Tully 

 limestone conld not have been formed from the remains of shells and 

 other calcareous organisms broken in situ, but that the lime mud must 

 have had a different origin, or else have been transported by currents to 

 this region from a distant point of origin. Chemical precipitation or 

 tlie growth and destruction of calcareous algae might account for a lime 

 accumulation of this kind, but thin sections of the rock show no evidence 

 of structure whicli would lend plausibility to either conclusion. The rock 

 has the characteristics of a fine lime mud, apparently of clastic origin. 

 TsTor are there anywhere in this region residual masses of algal origin, 

 such as generally are to be found in regions where limestones are formed 

 by these agencies. 



It appears, then, that the lime mud, of which the Tully limestone con- 

 sists, had its origin in some other region and was brought to its present 

 resting place by the currents of the Tully sea. The source of the lime 

 might be either an older limestone, the destruction of which furnished 

 the lime, or a reef mass of algal, coral, or other origin, the erosion of 

 which could furnish the lime. The first of these sources is negatived by 

 the fact that the formations subject to erosion during Tully time were 

 mostly argillaceous and siliceous sediments, calcareous beds being spar- 

 ingly represented in these formations. It would thus be impossible to 

 account for the comparative purity of the Tully limestone, as well as for 

 the absence of corresponding argillaceous and siliceous sediments into 

 which the limestone should grade laterally. The reef theory is open to 

 no such objections, for all that is necessary to assume is that the drainage 

 from the Hamilton lands, which were subject to erosion at that time, was 

 carried into another portion of the sea, where it could not interfere with 

 the development of a relatively pure limestone mass. Since lime muds of 

 the type which forms the Tully limestone can be carried in the sea for 

 great distances, the reef which was their source might have been far re- 

 moved from the present line of outcrop of these limestones, and indeed 

 might since have been entirely destroyed by erosion. 



Traced eastward from Tully, along the outcrop, the limestone is seen 

 to diminish in thickness with relative regularity, until it has disappeared 

 entirely as a limestone in the meridian of Smyrna, in Chenango County c 

 Prosser has been able, however, to trace the Tully fauna for a considerable 

 distance east of this point, its chief diagnostic member, Hypothyris 

 cuboides, occurring in a layer at the top of the Hamilton and just below 



