Fictitious Vegetable Impressions in Sandstone Rocks, 23 



of the bed, shewing very distinctly the nature of the effects 



to which I refer; A B being the . 



breastwork of sand, C, JJ, H#, shew- 

 ing the regular disposition of the 

 minute channels on the surface of 

 the deposit: these are invariably 

 broadest at the point where they 

 issue from the mass of sand, and 

 gradually diminishing as they pro- 

 gress, divide themselves alternately 

 into a fine network. Since it may with confidence be inferred, 

 that the cause to which these effects are due, would be in fre- 

 quent and extensive operation during those periods required 

 for the formation of our numerous sandstone rocks, it appears 

 to follow, that it may occasionally be necessary to distinguish 

 between these surface impressions due to the action of very 

 small streams of running water, and those due to actual im- 

 bedding of vegetable remains. It will readily be admitted, 

 that could an impression equally regular in its outlines, be 

 transferred to a mass of sandstone, it would be difficult to 

 resist the conviction of its organic origin, and as I have not 

 before seen any reference made to the production of such 

 impressions by the cause herein adverted to 5 1 trust the few 

 observations I have made, as they may tend to eliminate 

 error, will not prove uninteresting. It is easy to conceive a 

 geological catastrophe, which would lead to the immediate 

 enclosing of impressions made by running water in the mass 

 of a sandstone formation ; as for example, the covering of a 

 tract of country by volcanic mud or sand, or by the sudden 

 disruption of a lake, the waters of which were heavily charg- 

 ed with sediment or the deposit on the surface of the 

 ground of the sand held in suspension by rivers after heavy 

 floods.* 



* Some sandstones derive a slaty structure from these arborescent, or 

 as Professor Jameson calls them, dendritic delineations, which, however 



