426 NEW YORK STATE MUSEUM 



Luther, has made a series of traverses across this region, zig- 

 zagging from the Niagara escarpment at the north back and 

 forth along various meridians. It is perhaps not altogether a 

 contribution to the geology of this region to state that the 

 evidence obtained brings out quite clearly the fact that a proxi- 

 mate cause of this area of heavily timbered swamp land, which 

 the state has unavailingly attempted to redeem, is the removal 

 of vast amounts of soft shale at different geologic horizons, 

 leaving as the actual rock bottom of the depressions a pave- 

 ment or sill of heavy limestone; thus, by the removal of the 

 Rochester shale which lies on top of the Clinton limestone, 

 deep depressions running east and west along the strike of 

 these formations were produced, and hence we find that some 

 of the northerly branches of the swamp area, specially those of 

 the Oak Orchard swamp, rest on a bottom of limestone from 

 which this soft shale has been excavated. These areas are in 

 a certain measure cut off from the large area of the swamp 

 which has been produced by the removal of the soft Salina shale 

 from the limestone or dolomites pertaining to the Niagara 

 formation. Hence the great swamp area generally speaking 

 lies on a pavement of Lockport dolomite, and by the outcrop- 

 ping ridges of this dolomite it is more or less distinctly cut off 

 from the smaller swamp areas lying to the north. The removal 

 of these large amounts of soft rock may be freely ascribed to 

 erosion by stream action, and we find both in the Tonawanda 

 and Oak Orchard creeks — streams whose main courses lie 

 approximately east and west — a remnant of a force which would 

 produce and probably has produced depressions of this kind 

 along the strike of the rocks. While the removal of such large 

 quantities of soft rock lying between formations of harder and 

 more resistant texture may be looked on as the occasion for 

 the existence of these swamps, the cause of their present actual 

 extent and transgression of geologic barriers is doubtless to be 

 found largely in more recent damming of the waterways 

 required by the construction of the Erie canal, obstructing the 

 natural drainage of the whole territory and rendering the actual 

 run-off insufficient and incomplete. In an appendix to this 



