418 N. H. Darton — Magothy Formation of Maryland. 



Patuxent River region. — South of Odenton the Magothy 

 formation gradually thins but it extends to some distance be- 

 yond the Patuxent River before terminating. 



In the ridge just east of Bowie and again on the ridge be- 

 tween the two forks of the Patuxent there are outliers of 

 Magothy brown sandstones in turn capped by small areas of 

 weathered Severn beds. The Potomac formation in the adja- 

 cent slopes are typical variegated clays in greater part, but 

 there are also lenses of compact gra} r sands locally silicified to 

 white quartzites. 



The southwestern termination of the Magothy formation 

 is not clearly exposed and the outcrops along the Patuxent 

 are obscure. In the hills southwest of Bowie the Severn beds 

 lie directly on Potomac clays and are themselves cut out at 

 intervals westward by Pamunkey beds as far south as Wash- 

 ington. 



The thinning may be due to an actual decrease in thickness 

 of the original deposit or an overlap of its shore lines by a 

 later formation, but it appears to have resulted from an increase 

 southward of the erosion to which its surface was subjected in 

 the interval preceding Severn deposition. 



Original extent and thickness. — How far south the Magothy 

 formation may have extended is not known, and as its surface 

 has been eroded the original thickness is not determinable. 

 The location of the northwestern shore line of the formation 

 is not defined but it was probably very near the gravelly deposits 

 extending from Bowie to beyond Odenton. 



Definition. — The Magothy formation is a thin series of 

 arenaceous deposits lying between the Potomac and Severn 

 formations and separated from both by erosional unconformity 

 and great dissimilarity of character. There are local uncon- 

 formities at various horizons in the Potomac formation at the 

 base of some of its sand lenses but these unconformities are 

 due solely to current action and exist only within a restricted 

 area. I have studied many of these Potomac sand lenses and 

 found the sands grading laterally into clays or clays and sands 

 and these merging downward across the horizon of uncon- 

 formity into clays below. The unconformity at the base of 

 the Magothy formation is clearly not of this character nor is 

 the break at its summit, but both are in every way similar to 

 the erosion planes which bound all the other members of the 

 Coastal plain series. 



The age and equivalence of Magothy formation is not 

 known with any degree of precision but its stratigraphic posi- 

 tion places it in the early Cretaceous. It contains plant re- 

 mains at several localities notably in the lignitic members on 



