T<,1 



SALT LAKES OF NORTH AMERICA. 347 



Those forwarded by Dr. Francis Le Baron, are bedded 

 in fetid limestone of a very dark colour. The spaces 

 whence the shell had disappeared are sometimes filled 

 with white ealcarious spar. The appearance of the pe- 

 trifactions is thus very strikingly diversified* In other 

 cases, the shell itself, though altered or petrified, re- 

 mains. 



Madrepores, of various magnitudes and kinds, occupy 

 places in the strata of this ealcarious carbonate. The 

 central part of a very large one in my collection, exhibits 

 a kind of radiations intersected by concentric circles. 

 Some of the spaces or cells between them are yet empty, 

 and others filled with a more newly formed cal carious 

 substance. This probably belonged to a species now 

 extinct. 



A neat topographical description of this region -was 

 written in 1809, by Dr. Hugh Henderson. After having 

 been read before the Central Medical Society at Albany, 

 it was printed in the Medical Repository at New- York, 

 (vol. xiv. p. 21 27.) He states expressly, " that there 

 are such distinct traces of marine shells in all the stones 

 he had yet seen, that he cannot resist the belief that 

 either at the flood or some period since, this country has 

 been inundated by the waters of the lake." This intelli- 

 gent writer states in his memoir, the conjecture, that at 

 the Thousand Islands, the attrition of the water had 

 worn down the primitive rocks of granite, and reduced 

 the stream to its present dimensions. 



My own observation has assured me that to the west- 

 ward of the Little Falls on the Mohawk, remains of 

 oceanic animals are found, sometimes in limestone, some- 

 times iu argillaceous sbist, sometimes in very white sand- 



