128 
GEOLOGY OF THE THIRD DISTRICT. 
readily strikes the eye by its contrast with its associated rocks, and by the singular markings 
or impressions which it contains, some of which, and parts of all, strongly resemble the 
curling feathers of the tail of the male of our common barnyard fowl, or rooster. 
30. 
No. 1 of the wood-cut is the common form which belongs to this rock ; the curves pass or 
rise from a common centre, which is raised or depressed according as the upper or lower 
impression is examined. The curves usually have this peculiarity, that though their direction 
