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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Apr. 30, 



occurs are nearly flat ; they have, however, a dip to the eastward, 

 which is towards the limestone, the nearest development of which is 

 about a mile distant. Near Beauharnois the breadth of the Potsdam 

 belt is about five miles, and from this position it gradually widens 

 to the southward, the rock being traceable by many exposures, some 

 of them of considerable extent, on the one hand all the way to Kees- 

 ville, where it holds Lingula antiqua, and on the other to Potsdam 

 and farther to Hammond, where, as well as at Alexandria, Lingula 

 prima is met with, these Lingulce being hitherto considered the most 

 ancient evidences of organic life in America. 



4. Description of the Impressions on the Potsdam Sandstone, 

 discovered by Mr. Logan in Lower Canada. Bv Prof. Owen, 

 F.R.S., G.S. 



The evidence of the track and foot-prints submitted to my exami- 

 nation by Mr. Logan consists of a slab of the sandstone with eighteen 

 impressions of the right fore and hind feet, and ten of the left fore 

 and hind feet, with a faint trace of a broad track between them, and 

 of six casts in plaster of Paris (each cast being twenty-six inches 

 by fifteen inches) of successive portions of the impressed rock, 

 and each cast exhibiting from twenty-six to twenty-eight impressions 

 of both the right and the left feet, with the broad and shallow me- 

 dian channel better marked in most of the casts than on the portion 

 of the sandstone. The successive foot-prints are more numerous than 

 any which have been previously discovered, and the circumstance of 

 the corresponding prints recurring at regular intervals affords the 

 strongest proof of their having been made by successive steps. 



The foot-prints are in pairs, and the pairs extend in two parallel 

 series, with the channel exactly midway between the right and left 

 series. 



The outer impression of each pair is the largest, being about an 

 inch in diameter, and is commonly a little behind the inner one, 

 which is about eight lines in diameter. Both are short in proportion 

 to their breadth, with faint indications, in some, of divisions at their 

 fore-part. 



The two prints forming the pairs here and there are confluent or 

 touch each other, but are commonly from four to six lines apart ; and 

 the pairs of the same side succeed each other at intervals varying 

 from one inch and a half to two inches and a half, the common di- 

 stance being about two inches. The interval between the right and 

 left pairs, measured from the inner border of the small prints, is three 

 inches and a half, and from the outer border of the large prints is 

 seven inches. The median track is one inch and a quarter in breadth, 

 and sinks about two lines below the surface where deepest impressed ; 

 varying in depth, but not in its relative position to the right and left 

 foot-prints ; and being deepest where the pairs of foot-prints are con- 

 fluent and at shortest intervals ; at which parts the median channel 



