376 :\n:s()Z()i(' floras ok rMri:i) statks. 



to run under it to the south, hut even this is nuich older than the l)eds 

 on the Severn Ifiver in Maryland in whicli occur his type sections of 

 the All)irupean. 



My own studies in the formation were resumed witli the openintj 

 of the field season of 1892. Early in May Mi'. l)a\id White accom- 

 panied me on an excursion to P'redericksburg and the region adjacent. 

 We first studied the contact of the Potomac with the underlyhig crys- 

 tallines on the Ivappahannock, on Fall Run al)ove lalmouth, and on 

 Hazel Run to the south of Fredericksburg, and usually found a bed 

 of clay underlying the freestone. A number of instructive sections 

 were made. Above the freestone occur heavy beds of loose sand. We 

 then followed the Rappahannock down in a rowljoat from P'redericks- 

 burg to the Eocene contact at the Marl Mill, 6 miles below. This affords 

 a fine section. The dip to the southeast is about 50 feet to the mile 

 and the distance in a straight line from the crystalUne contact to the 

 Eocene contact is about 6 miles, giving the Potomac a thickness of 300 

 feet. We were able to measure only a little over 200 feet, but theie 

 was evidence of erosion at seA'eral points. The 200 feet measured were 

 as follows: 



Section of the RappahamMck River at and hehu: Frederickshurq. 



3. Loose iirgillaccous, mostly white or veHowish, .sand with tliin clay seam.s, l)ecoiniii^ daikcr and lijiiii- 



lifcrous above, and iinconforniably overlain by the Eoeen* (Panunikey ) marl .50 



2. Coarse, feldspathic, conglomeratic sandstone with lenses, nodules, and pellets of fine white clay, and 



with casts and molds of steins, lojjs, and indeterminable plants KM) 



1. Red, pink, and purple to white clay, currying lignite and (on Fall Knn) lignitized logs; resting uncon- ■ 



formably upon the crystalline rocks .50 



Total exposure 200 



The clay disappeared beneath the water of the river opposite Pratts 

 Rock, the sandstone 3 males below that point, the sand at Tl■a^•elers 

 Reach, and the last of the darker lignitic beds half a mile above the 

 Marl Mill. Back from the river the higlier country in all directions 

 from Fredericksljurg is covered with a relatively modern deposit, pi-ob- 

 ably the Lafayette, while the bottom lands usually show a bed of Colum- 

 bia l)iick clay. For these reasons the geological map of this region is 

 colored for these formations only, giving no proper idea of the geology. 



Leaving Fredericksburg on the 5th we explored the general region 

 to the north as fai- as Stafford Court House along the western maigin 

 and found the plavs almost evervwhere underhing the sandstone. \\'e 



