REPORT OF THE STATE PALEONTOLOGIST 1901 523 



over the area which must be ascribed to the exposures of Lock- 

 port dolomites where at least the dolomites must be in main 

 the underlying rock, the considerable, often thin, broken and 

 interrupted extensions of the swamp areas. The rock ridge 

 showing just north of Churchville and North Chili thence west- 

 ward beyond Shelby, a ridge composed of the Lockport dolo- 

 mites, may hold the key to the artificial drainage of the major 

 swamp areas. The great body of the swamp north and south 

 covers not only the width of the Lockport dolomite but also 

 that of the Rochester shale and extends farther to the north 

 than it is proper to draw the dividing line between the Clinton 

 and Medina. From this consideration then it becomes evident 

 that the heterogeneous character and the differential erosion of 

 the underlying rocks are not a sufficient cause for the present 

 distribution of the swamp areas, and while this is doubtless 

 an efficient contributory cause for the actual existence of these 

 extensive depressions, their original boundary has been exag- 

 gerated by artificial obstruction to drainage. 



