340 ANNUAL OP SCIENTIFIC DISCOVERY. 



soy, described by Dr. Harlan, were in every respect analogous to those of 

 the Maestricht reptile, and that the deposit was equivalent to the Maestricht 

 bed. The Blackdown grecnsand of Dr. Fitton *has in its fossil mollusca a 

 very strong resemblance to our greensand fossils; and as D'Orbigny makes 

 this formation an equivalent to his Ceuomanien, there is some evidence that 

 the New Jersey greensand maybe on the same horizon; for, according to 

 D'Orbigny's tables, the genus Bclemnites ceases with the Ce'nomanicn, and 

 we have abundance of that genus in our greensand formation. If he be 

 correct as to the decadence of the Cephalopoda, then we could not place this 

 formation higher up in the series than his Cenomanien, which is the " Glau- 

 conie crayeuse " of Brogniart, found at Cap le Heve, in France, the Black- 

 down greensand of Fitton, and the Upper greensand, of Mautell in the south 

 of England. 



Under all the information we have, however, from the various investiga- 

 tions made by so many distinguished geologists, I think the evidence is in 

 favor of D'Orbigny's opinion, that the greensand formation, from which 

 the remains of the Hadrosaurus were exhumed, belong to his Se'nonien; but 

 it may prove, upon further examination, to be a little lower in the Cretaceous 

 scries. 



ON THE INFUSORIAL DEPOSITS OF THE TERTIARY OF VIRGINIA. 



At a recent meeting of the Boston Xat. Hist. Society, Prof. W. B. Rog- 

 ers presented some masses of Infusorial earth from the Tertiary strata of 

 Virginia and Maryland, and gave a description of the geological and other 

 conditions in which this and the associated deposits exhibit themselves in and 

 near Richmond, in the former of these states. 



The Tertiary formations which underlie the wide plain extending from the 

 seaboard to the eastern margin of the granitic and gneissoid rocks, approach 

 their termination along this meridian in a series of strata which are sepa- 

 rated by only a short interval from the irregular granitic floor. A little fur- 

 ther toward the west they reach their boundary, partly by a rapid thinning 

 away, and in part by abutting, along the hill-sides, against the indented shore 

 of these ancient rocks, here rising to the level of the general upland surface. 



In the deep ravines leading into the valley of Shockoe Creek, especially 

 on its western side, we meet with several extensive exposures of the Terti- 

 ary strata, one of which embraces nearly the whole thickness of both the 

 Eocene and Mciocene formations as locally developed in this neighborhood. 

 In all these localities the infusorial deposit is found occupying a position im- 

 mediately above the upper limit of the Eocene strata or separated from it 

 by a thin layer of whitish or of more or less ferruginous clay. Like the 

 associated beds, it fluctuates in thickness as traced from one neighboring 

 exposure to another, varying from twenty to upwards of thirty feet at the 

 different localities on the north side of the valley, and presenting, where 

 measured some years ago, on the opposite or Church-Hill side, a thickness 

 of nearly fifty feet. In addition to the microscopic fossils, which in a more 

 or less perfect condition makeup so lanrc a portion of the mass, this deposit 

 presents a few casts of shells of well-known Meiocene forms, of which the 

 Astarte undulata may be mentioned as of the most frequent occurrence. I!: 

 also contains imperfectly preserved remains of a slender creeping plant, as 



* Strata bolow the chalk. 



