Fossil Footprints of the Connecticut Valley. 165 



most favorable time is when the sun's rays fall obhquely upon 

 the stratum and project a shadow into the shallow depressions.* 

 I do not find them, except upon smooth surfaces — a fact indica- 

 ting that the sedimentary elements of the face of the rock were 

 deposited when nearly in a soluble state, and that the impress 

 was made at the favorable period when the drying process allow- 

 ed the impression to be most perfectly taken as well as retained. 

 Ichnolites are frequently associated with rain-drop impressions, 

 and I have always observed that when these are perfect, the ani- 

 mal vestiges are remarkable for beauty. I observed during the 

 past summer where a pool of water, the result of a shower, had 

 gradually subsided, the surface of the earth was coated with a 

 thin, shining, plastic sediment, which at first did not retain im- 

 pressions ; but in a few days a slight shower pitied the surface 

 completely, and footprints of frogs, birds, and dogs were ex- 

 quisitely retained, illustrating with great force the exact process 

 whereby ancient footprints were impressed and preserved, I re- 

 moved samples containing both rain-drops and footprints, which 

 are now in ray cabinet, and are of the solidity of unburnt 

 brick. I allude to this subject because it is important to the ob- 

 server ; it is a guide that may possibly save him from fruitless 

 toil. As a general thing, a smooth glossy surface free from grit 

 is most promising ; while coarse masses with granular surfaces, 

 even though stratified, are usually barren. The habit of observ- 

 ing correctly can be acquired only by labor, and these hints may 

 not be useless in a practical sense to beginners in discriminating 

 between the conditions that indicate the probability of success 

 or the certainty of disappointment. 



My collection of ichnolites for the past year has not been ex- 

 tensive, yet it comprises examples of peculiar interest. I have 

 with Mr. Marsh obtained from a locality thirty miles distant from 



* Since this article went to press, in examining a slab of superb Ornithichnites, 

 by candle light, I was surprised to discover two rows of extremely minute impres- 

 sions which had hitherto escaped my observation. When the rays fell in a direc- 

 tion nearly horizontal, the impressions were perfectly distinct. Both examples 

 were those of quadrupeds of the delicate variety illustrated by fig. 2 upon the 

 plate. One of them consisted of five impressions corresponding in size and stride 

 with fig. 2; but the other consisted of seven pairs of impressions, not one half as 

 large, the stride being only three inches. This is by far the most diminutive ex- 

 ample of fossil footmarks yet discovered, requiring a magnifying power to appre- 

 ciate it correctly. Upon another portion of the same stratum was an example of 

 this variety twice larger than fig. 2, distinct, with a stride of seven inches. 



