Miscellanies. 183 



Virginia, (second series,) by Prof. William B. Rogers, and Prof. 

 Henry D. Rogers," reported in favor of the publication of the Memoir, 

 which was ordered accordingly. 



The object of this communication is to describe the geology of the 

 peninsula embraced between the Potomac and Rappahannock rivers, 

 extending from the Chesapeake Bay to the limit of tide water, near 

 Fredericksburg. 



This area consists almost exclusively of the two great divisions of 

 the Tertiary Deposits of Virginia, namely, the Eocene and Miocene 

 formations. 



The paper commences with a sketch of the topographical features 

 of the peninsula, making allusion, among other points, to the interest- 

 ing terraced configuration of the land bordering the valleys of the two 

 rivers. It then proceeds to delineate the boundaries of the Eocene 

 and Wliocene formations. The Eocene is shown to occupy the west- 

 ern part of the peninsula, overlapping at its western eAge the secon- 

 dary sandstone of Fredericksburg, and extending eastward with a very 

 gentle eastern dip beneath the overlying Miocene deposits, until it 

 finally disappears below the level of the tide near the mouth of Chin- 

 goteague creek on the Rappahannock, and Mathias's Point on the 

 Potomac. The Miocene spreads eastward from the line connecting 

 these two localities to the termination of the peninsula ; while some 

 of its lower beds extend west of the same line into the Eocene dis- 

 trict, where they are confined, however, to the highest portions of the 

 land. 



After offering numerous details relating to the range and limits of 

 these two divisions of the Tertiary Deposits, the paper treats in the 

 next place of the arrangement and composition of the Miocene strata, 

 which are shown to possess a close general analogy in these respects 

 to the Miocene beds of the peninsula of the York and James rivers, 

 described in a former communication. The two most interesting 

 points of agreement are the occurrence of the blue marls low down in 

 the series, and the presence of the thin band of ferruginous rock sepa- 

 rating the Miocene from the overlying diluvium. 



In general the blue marl at the base of the Miocene, is the most 

 replete in fossils, though towards the eastern extremity of the penin- 

 sula, shells, &c., abound in the upper sands and clays. Usually the 

 upper beds of the Miocene in this district are destitute of fossils, 

 though full of their casts and impressions. 



These strata consist generally of light colored sandy clays, distin- 

 guished by a sulphurous smell, and an acid and styptic flavor. Car- 

 bonate of lime is not abundant, but the sulphate of lime occurs some- 

 times in valuable proportion. Sulphate of iron, sulphate of alumina, 



