214 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mar. 24, 



2. Description of the Impressions and Foot-prints of the 

 Protichnites from the Potsdam Sandstone of Canada. 

 By Prof. Owen, F.R.S., F.G.S. &c. 



[Plates IX. to XIV. A.] 



Of the extensive series of foot-prints found under tlie circumstances 

 described in the preceding communication, the originals of some and 

 good plaster-casts of more have been brought over with much labour 

 and expense by their discoverer, Mr. Logan, and of these I have se- 

 lected the best-marked and most intelligible portions for the following 

 descriptions. 



1 . Protichnites septem-notatus. PI. IX. 



The subject, which for the convenience of reference I have so 

 named, consists of a series of well-defined impressions, continued in 

 regular succession along an extent of 4 feet ; and traceable, with an 

 inferior degree of definition, along a further extent of upwards of 2 feet. 



These impressions (see Plan, PL VIII. A. 6) are represented by 

 plaster- casts. 



In the first-selected extent of 4 feet there are thirty successive 

 groups of foot-prints on each side of a median furrow, which is alter- 

 nately deep and shallow along pretty regular spaces of about 2\ inches 

 in extent. The number of prints is not the same in each group ; 

 where they are best marked, as in PI. IX. 1 X, we see 3 prints in one 

 group, a, oJ, «", 2 prints in the next, 5, h\ and 2 in the third, c, c', 

 which is followed by a repetition of the group of 3 prints, «, a\ a". 

 But, in some instances, the outer print of the third set is divided, as 

 at 1 72, c', c", making the numbers in the three successive groups 3, 

 2, 3, instead of 3, 2, 2 : the three groups of impressions are, however, 

 notwithstanding this occasional variety, recognizably repeated in suc- 

 cession along the whole series of tracks on both sides of the median 

 groove*. 



The principal foot-prints are disposed in pairs, placed with different 

 degrees of obliquity, in each of the three groups, towards the median 

 track ; the innermost print in the second, ^, and third, c, pairs, which 

 are best marked, being usually rather more than half the size of the 

 outer print, V and c'. 



The two foot-prints of the same pair are a little further apart from 

 each other, in the three succeeding pairs, as at a\ a", 5, h\ c, c', espe- 

 cially in the second and third groups of each set ; the two forming 

 the pair «', a" again approximating in the next series, and the pairs 

 b, V and c, c' diverging in the same direction and degree ; and this 

 alternate approximation and divergence is repeated throughout the 

 entire series of the present tracks. 



* Should these descriptions express more or less than is shown in the Plates, 

 the reader will be kind enough to bear in mind that they were penned after re- 

 peated examinations of the originals by varied applications of artificial and natural 

 lights, and express the sum of the results of such comparisons extended over the 

 entire series of tracks ; whilst the able artist has given the effects of one light and, 

 shade only, as seen on one portion of the track. 



