82 The Lowee Cretaceous Deposits of Maryland 



wise be called u]3on to explain cross-bedding, although it would seem that 

 the latter class of deposits are practically negligible when the materials 

 are considered as a whole. The quickened streams at the inauguration of 

 the Patuxent built out alluvial fans with comparative rapidity and af- 

 forded little opportunity for the preservation of terrestrial vegetation 

 or of the aquatic life of the Patuxent rivers or lakes. The fossil plants 

 which are so sparingly distributed in the Patuxent represent for the most 

 part fragments of coniferous stems or coriaceous bits of foliage which 

 successfully resisted the trituration of the coarse sediments. Only one 

 Patuxent exposure, that at Fredericksburg, Virginia, has furnished an 

 extensive flora, and this was contained in a single somewhat more argil- 

 laceous lens of very limited extent. Elsewhere a considerable flora has 

 been found in redeposited masses or balls of purer clay, which were 

 evidently transported from their original place of deposition in the 

 quiet waters of some Weverton oxbow or lake, and therefore antedate in 

 their origin and their contained flora that which was contemporaneous 

 with their final deposition in the Patuxent sands. That the contained 

 flora is not appreciably different from that of the balance of the Patuxent 

 flora indicates that this time interval, while long according to human 

 standards, was short when measured in terms of geological processes. 

 Such meagre fragments of the aquatic life of the Arundel and Patapsco 

 epochs as are preserved, a few almost undeterminable fresh-water gastro- 

 pods, tiny pelecypods and unios, indicate that conditions similar to those 

 outlined above persisted until the close of the Potomac. 



The Patuxent deposits, like those of the succeeding Arundel and 

 Patapsco formations, reflect in a large measure the character of the 

 Piedmont materials which lie immediately to the westward. Where these 

 materials were highly feldspathic the sediments are strongly arkosic. 

 This is a very characteristic feature of the Patuxent deposits, and one 

 which continues unchanged as far as eastern Alabama, a distance of 

 several hundred miles. Where gabbros or other rocks rich in the iron 

 minerals are found near the eastern margin of the Piedmont, as in the 

 vicinity of Baltimore, the derived sediments are ferruginous, and this 

 is especially noticeable in the concentration of the iron in the Arundel 



