J, D. Dana on American Geological Histo?y. 315 



York beds of this rock had afforded only a few mollusks ; but 

 the investigations of Owen and others have added the remaining 

 tribes ; and this diversity of forms is confirmed by Barrande in 

 his Bohemian researches.* 



Among the genera, while the most of them were ancient forms 

 that afterwards became extinct, and through succeeding ages 

 thousands of other genera appeared and disappeared, the very 

 earliest and most universal was one that now exists, — the genus 

 Lingular, — thus connecting the extremes of time, and declaring 

 most impressively the unity of creation. Mr. T. S. Hunt, of the 

 Canada Geological Survey, recently discovered that the ancient 

 shell had the anomalous chemical constitution of bones, being 

 mainly phosphate of lime ; and afterwards he found in a modern 

 Lingula the very same composition, — a further announcement 

 of the harmony between the earliest and latest events in geolog- 

 ical history.f 



This earliest sandstone, — called in New York the Potsdam 

 sandstone, — and the associated Calciferous sand-rock, mark off 

 the First Period of the Molluscan Age, — the Potsdam Peeiod, 

 as it may be called. :£ 



Next followed the Trenton Period, — a period of limestones, 

 (the Trenton limestone among them,) equal to the earlier beds 

 in geographical limits, and far more abundant in life, for some 

 beds are literally shells and corals packed down in bulk ; yet 

 the species were new to the period, the former life having passed 

 away ; and even before the Trenton Period closed, there were 

 three or four epochs of destruction of life followed by new crea- 

 tions. The formation of these limestone beds indicates an in- 



* The Lingula prima and L. antiqua are the Mollusks referred to as occurring- in 

 the New York beds. The discoveries by Owen, in the vicinity of the Falls of the 

 St. Croix, Minnesota, and on the Mississippi, were published by him in his Report 

 on a Geological Reconnoisance of the Chippewa Land District of Wisconsin and 

 the Northern part of Iowa, Washington (Senate Document), 1848, p. 14, and subse- 

 quently in his quarto Report on Wisconsin, &c, of 1852. The fossils he mentions 

 in the latter work are species of Lingula, Obolus, Orbicula, Orthis, several forms of 

 Crinoids, and large Trilobites referred mostly to the new genus JDikelocephahis. 

 The species as named are, Lingula antiqua, L. prima, L. pinnaformis Owen, L. am- 

 pla Owen, Obolus Apollinis (?), Orbicula prima 0., Dikelocephalus Minnesotensis 

 O., J). Miniscaencis 0., D. (?) lowcnsis O., D. granulosus O., D. Pepinensis 0., Loncha- 

 cephalus Chippewaensis 0., Crepicephalus (?) Wisconsensis O., C. Miniscaensis O., 



Prof. W. B. Rogers in the last number of this Journal (p. 296), announced the 

 discovery of the Trilobite Paradoxides Harlani of Green (P. spinosus of Barrande) 

 in slates ten miles south of Boston, Mass., a species found by Barrande in his proto- 

 zoic or earliest fossiliferous rock of Bohemia, — thus adding a new species to the 

 American protozoic Fauna, and the largest yet discovered, the length of some of the 

 specimens exceeding a foot. Prof. E. Emmons announces also (Meeting of Amer. 

 Assoc. in August last, at Albany) the discovery of a large Cyathophylloid coral in 

 the lowest fossiliferous rocks of North Carolina. The exact age of the rock however 

 is yet uncertain. — See a notice beyond in this number. 



f Am. Jour. Sci., [2], xvii, 235, (1854). 



f Through the comparisons of Prof. Hall, it is now well known that the " Lower 

 Magnesian Limestone" of the west and a sandstone with which it alternates, corres- 

 pond to the Calciferous sandrock of New York. 



