250 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Mai'. 5, 



by Dale Owen* for the oldest known Trilobites of America, which 

 were found in the Potsdam sandstone of St. Croix, Minnesota. 



The far more transverse form of our fossils, and the entire want 

 of annulation on the axis or side-lobes, are sufficient to indicate a 

 distinct genus ; and I dedicate the species to Prof. Ramsay, who has 

 done so much to clear up the history of the Longmynd. 



Locality. Ridge north of Callow Hill, Little Stretton. This fossil 

 occurs with the next described. 



Marks of ? PI. IV. fig. 4. 



There are numerous hollows on the surfaces of the beds, which 

 greatly resemble the impressions of Rain-drops. But they are less 

 regular, less equal in size, and, although generally oval and lying in 

 the same direction, have no ridge thrown up in front of them. It is 

 impossible, however, to say they have not been caused by primeval 

 rain ; and Sir Charles Lyell, who examined them, was much struck 

 by their resemblance to those he has figured and described. 



Across the same surfaces run very frequently raised thread-like 

 lines (PI. IV. fig. 4, «) in the same direction as the longer diameter of 

 the spots. Sometimes these lines are simply parallel, at others they 

 are branched, at others interrupted and fading off. But they are 

 sufficiently parallel and uniform in their direction over the bed to 

 make it probable that they are lines of mineral structure, rather than 

 anything organic, and I believe, too, that the drop-like hollows may 

 be due to gaseous bubbles, or to the decomposition of small concre- 

 tions, rather than that they indicate the marks of ancient showers. 



Locality. — Carding Mill, in the base of the red or purple sand- 

 stone (No. 4). 



Ripple Marks (with thin mud-coating 1) . PI. IV. figs. 5 &; (i. 



The surfaces of very many of the beds are, as above noticed, co- 

 vered with ripple- or current-marks ; this is particularly well seen 

 about the small Waterfall called Light-spout, above Church Stretton. 



Dark grey micaceous flags are there easily split into thin layers ; 

 and on these the ripple-hollows are generally stained with a thin film 

 of protoxide of iron. Numerous radiating furrows, in the form of 

 very fine branched lines, run from the margin toward the centre of 

 these hollows or across them ; the smaller ones near the edge run- 

 ning into the larger, just as brooks run into rivers. The lines are 

 always impressed on the upper surface of the bed (i. e. in the faces 

 dipping westward), so far as this could be ascertained, and are ele- 

 vated threads on the casts of these hollows upon the lower surfaces ; 

 the edge of the hollow (PL IV. fig. 5) being concave or convex in 

 each respective case. These ripple-marks have suffered, of course, 

 all the contortions of the beds ; and hence are puckered (c), flat- 



* Report of Geol. Survey of Wisconsin, Iowa, and Minnesota. Philad. 1852, 

 p. 573, pi. 1. 



