IN THE RED SANDSTONE OF POTTSVILLE. 313 



marks or grooves on as many ripple lines, the crests of which lines are elevated about 

 halt* an inch above the intermediate depressions. The tail was evidently not a thick one, 

 and the animal must have had a distinct and perfect step, and not a half swimming 

 motion, as in the crocodilians, there being no trace of the dragging of the feet. The tail 

 must have been considerably elevated, as the alternate tail-impressions show that a vibra- 

 tion actually took place at every step, the four grooves not being in a direct line, but 

 each one approaching its nearest "foot-mark" to the right or the left, alternately, and 

 iherefore never precisely on the central line between the two rows of the foot-marks. 

 These facts prove that the animal which left its imprint in this ancient sandstone stood 

 much higher on its legs than the Crocodilus or the Monitor, and likely was not so long in pro- 

 portion to the size of the feet. It is well known that the alligator leaves no foot impres- 

 sion in the mud, hut simply a large furrow, made by the ventral and caudal portions. 

 The form of the foot impressions are, however, very similar to that which is received by 

 the mould in clay of the Alligator Mississippiensis, specimens of which arc in the collection 

 of the Academy of Natural Sciences of Philadelphia. If an opinion might be hazarded 

 as regards the probable size of the animal, based on this meagre diagnosis, I should 

 suppose it might reach as much as seven or eight feet in length. 



The " ripple-marks," as observed before, covered the whole surface of the exposed 

 part of the rock, six by twelve feet. Their crest-lines are generally seven or eight inches 

 apart, and they swell up gently in nearly parallel lines, but falling off and recommencing 

 again, give an irregular appearance to the surface, but which is altogether harmonious. 



The "rain-drop pits" are rather large and nearly round, showing a tranquil state of 

 the atmosphere when the rain descended. They covered the whole surface, and are not 

 very deeply impressed. 



In regard to the geological position of the "foot-marks" of this reptilian quadruped, 

 having had no reason to doubt my former views, originally expressed in the Proceedings 

 of this Society, I shall state it here nearly in the same words. The discovery was of 

 great interest from the fact that no such animal remains had before been discovered so 

 low in the series. Those described by Dr. King, in the great western coal-field, which 

 naturally created great interest, are only eight hundred feet below the surface of the coal 

 formation. (No. 13, of Prof. Rogers.) The position of the Pottsville "foot-marks" is 

 about 8500 feet below the upper part of the coal formation there, which is 6750 feet thick, 

 according to Professor Rogers, and they are in his "Red Shale formation, "(No. 11,) 291!) 

 feet thick, the intermediate silicious conglomerate (No. 12,) being stated by him to be 1031 

 feet thick at Pottsville. These measurements would bring these foot-marks about seven 

 hundred feet below the upper surface of this " Red Shale Formation," (No. 1 1,) which is the 

 Old Hrd Sandstone of Mr. Taylor, Mr. Hall and other geologists of the New York Sur- 

 vey,* and now known as the Devonian of Sedgwick and Murchison. It has been well 



" Bee R. *'. Taylor " On the Carboniferous Series of the United States;" " Report of the Dauphin and Sus- 

 quehanna Coal Company;" "Geological Chart of the Silurian Rock Formations of North America," MSS. 1 8 17, 

 in the Library of Acad, of Nat. Sci., &c, James Hall, " Geology of New York," Part 4, pp. 278, 510, <fec, 

 and other of these New York Reports. 



