W. H. Darton — Magothy Formation of Maryland. 407 



Wald in Styria.* The original reference to the first has not 

 been accessible to me, and the second contains no mention of 

 the mineral's properties. 



The Canaan mineral is thus shown to belong to the talc 

 family by its chemical composition as well as by most of its 

 physical and optical properties. That it is a somewhat distinct 

 variety is shown by its high percentages of lime and alumina, 

 by its low fusibility and easy decomposability by acid, and by 

 its exceptional rose color. 

 University of Wisconsin. 



Akt. L. — The Magothy Formation of Northeastern Mary- 

 land ; by 1ST. H. Darton, U. S. Geological Survey. 



Contents : Introductory. General relations. The Magothy Formation'. Dis- 

 tribution. General features. East of Chesapeake Bay. Magothy River region. 

 Severn River region. Odenton region. Patuxent River region. Original extent and 

 thickness. Definition. Synonomy. Economic Geology. History. 



Introductory. 



In this paper there is described an arenaceous formation not 

 heretofore discriminated, lying between the Potomac and 

 Severn formations in the upper Chesapeake Bay region. 



Up to 1891, when I published my memoir on the Mesozoic 

 and Cenozoic formations of eastern Virginia and Maryland,! I 

 had given but little attention to the details of the geology of 

 northeastern Maryland and believed that there was but one 

 physical gap between the Potomac and Severn formations. 

 Later studies in this region have led to the discovery that a 

 series of sands and brown sandstones which I formerly sup- 

 posed to be a local upper member of the Potomac formation, 

 is separated from it by a continuous erosion plane, and consti- 

 tutes a distinct formation. 



As this formation is excellently exposed on the Magothy 

 Piver, and partly for want of a better name it has been desig- 

 nated the Magothy formation. The general features of its dis- 

 tribution in Maryland are shown on the accompanying map. In 

 the course of a few weeks a geological map of Maryland will 

 be published by the State on which the lower boundary of this 

 formation will be represented on a larger scale, and later its 

 distribution west of Chesapeake Bay will be shown in detail 

 on atlas sheets now in course of publication by the U. S. 



* Rumpf, Ueber krystallisirte Magnesite aus den nordostlichen Alpen, Tscher- 

 mak's Mill. Mittheil., 1873, p. 271. 



f Geological Society of America, Bull., vol. ii, pp. 431-450, pi. 16. 



