﻿192 PORCELAIN EAETH. Jult, 



chemists could detect any nutritious matter in it. 

 Neither have I been able with the microscope to 

 discover in it the remains of any infusorial animals.* 

 Mr. Nuttall speaks of a similar substance under 

 the name of 2?inh-clay^ which he observed in the 

 lignite deposits on the Arkansa. It is known gene- 

 rally among tlie residents at the fur posts on the 

 Mackenzie by the appellation of " white-mud," and 

 is used for whitewashing houses, and also, when 

 soap is scarce, for washing clothes. 



In one place in the vicinity of the burnt cliff 

 where the leaves were found, several beds of porce- 

 lain-earth occur from two to three yards thick, and 

 apparently replacing the sandstone of other parts 

 of the formation. It has a whitish colour, and at 

 first sight looks like chalk, but some of its beds 

 have a greyish hue from the quantity of carbona- 

 ceous matter disseminated in them. Its texture is 

 fine-granular ; it adheres slightly to the tongue, 

 yields readily to the nail, is meagre, and soils the 

 fingers slightly. Besides the coaly matter, it con- 

 tains, also, a few minute scales of mica, and some 

 of quartz. It is not plastic, and becomes more 

 friable when moistened with water ; neither does it 

 effervesce with acids. This lignite formation extends 



* Baron Humboldt mentions a tribe of Indians residing on 

 the Orinoco, wlio eat large quantities of clay when food is 

 scai'ce. 



