008 EXPEDITION TO THE 



seen. In this bed the workmen state that they find sub- 

 stances resembling their catfish, (Silurus, Linn.) and 

 which they consider as petrifiictions of the same ; we saw 

 nothing of the kind, neither could they discover any at 

 the time we were there. We at first, however, thought 

 they had probably observed icthyolites, but a subsequent 

 and more minute description of the objects observed by 

 the workmen, satisfied both the naturalists, that they were 

 probably not organic remains, but mere accidents of frac- 

 ture, or lusi naturse. Independent of the building stone 

 which it yields, this bed is likewise valuable, as producing 

 the best lime of any found in the vicinity. Immediately 

 under this bed of limestone, in parallel stratification, we 

 observed the sandstone which constitutes the principal 

 mass of the bluff, being about sixty feet in thickness. It is 

 a very friable stone, and in some cases the grains, of which 

 it is formed, are so loosely united, that it appears almost 

 like sand. Every fragment, if examined with care, seems 

 to be a regular crystal, and we incline much to the opinion 

 that this sandstone must have been formed by a chemical 

 precipitation, and not by mere mechanical deposition. 

 The process of its formation may have been a very rapid 

 one, such as is obtained in the manufacture of fine salt, 

 and to this may be attributed the circumstance of its loose 

 texture. The grain is very fine ; its colour is white, some- 

 times a little yellowish, in which case, it resembles in tex- 

 ture, colour, &c. the finer varieties of Muscovado sugar. 

 The loose texture of the rock is probably the cause of its 

 presenting but few indications of stratification. The rock 

 which we have just described, rests upon a slaty limestone, 

 which has a striped aspect; the stripes or zones are curved. 

 This limestone appears to be very argillaceous, and is a 

 little softer than the preceding; its structure is quite 



