62 The Lower Cretaceous Deposits op Maryland 



deposition of Patuxent sediments has been elsewhere described as the 

 Weverton peneplain. Monadnocks rise from its surface, as at Grays 

 Hill, now surrounded by Potomac deposits. These underlying rocks m 

 Maryland consist, as far as known, only of crystalline rocks of early 

 Paleozoic and pre-Paleozoic age, although both farther north and south 

 the Newark formation of Triassic age here and there reaches to the 

 Coastal Plain border. The slope of this ancient surface which has been 

 regarded as of late Jurassic or early Cretaceous age, is quite uniformly 

 about 75 feet in the nlile towards the southeast, although local differences 

 occur due to the irregularities of the surface previously described. 



The Patuxent formation is sometimes irregularly overlain uncon- 

 formably in Maryland by the Arundel formation, which apparently occu- 

 pies post-Patuxent drainage lines that had been warped before the 

 deposition of the Arundel sediments. Covering both formations un- 

 conformably, and in the absence of the Arundel resting directly on the 

 Patuxent formation, is the Patapsco formation, which in Virginia, where 

 the Arundel formation is absent everywhere, comes in contact with the 

 Patuxent formation. In the absence of both of these formations of the 

 Potomac Group later formations of Upper Cretaceous, Tertiary and Qua- 

 ternary age are found overlying the Patuxent deposits unconformably. 



The internal structure and stratigraphy of the Patuxent formation is 

 at times very complex, more so than that of any of the other Coastal 

 Plain formations. Contemporaneous erosion planes, very coarse and 

 steeply inclined cross-bedding and alternations of extremely dissimilar 

 and sharply demarked beds and lenses in irregular attitudes, although 

 not the rule, are not at all uncommon. 



At times small folds occur in the beds in contact with the crystalline 

 rocks which are apparently due to local expansions in the latter, as the 

 result of their hydration. An interesting fold of this character is seen 

 in the pits of the Maryland Clay Company at Northeast, Cecil County, 

 as the result of the kaolinization of the feldspathic rocks. 



To what extent the beds have been subjected to larger structural 

 changes cannot be readily determined. The abnormalities in dip in the 

 vicinity of the Fall-line have iDeen already referred to, and the possibility 



