PHYSICAL IMPRESSIONS. 
The third great division of impressions in the 
sandstone rocks is called PuystcaL, meaning those 
made by inanimate and unorganized substances; such 
are rain-drops, ripple-marks, and coprolites. 
1. Marks of rain-drops, described on page 20, 
appear to be quite common. We have two or three 
specimens in relief, and as many in depression. They 
occur as follows: Ist, on the upper surface of the 
slab first described ; 2d, on that of the Platypterna ; 
3d, on that of the Aithyopus Lyellianus; 4th, on that 
of the Brontozoum Gracillimum ; 5th, on that of the 
/Ethyopus Minor; 6th, on that of the Anomcepus 
Scambus; 7th, on the recent clay; also in one small 
hand-specimen, and in a second containing two fishes. 
They show that, in those ancient periods when the 
Brontozoum Giganteum and the Otozoum resided in 
these parts, showers were frequent, and probably 
abundant for the supply of the wants and the grati- 
