34 THE PLIOCENE AND PLEISTOCENE DEPOSITS OF MARYLAND 



Post-Later Columbia elevation and erosion. 



Present depression and deposition. 



N. H. Darton took up the investigation of the surficial deposits at 

 the point where McGee left them. His publications on this subject began 

 in 1891 and extended down to 1901. During these few years Darton 

 added greatly to our knowledge of the Lafayette and Columbia deposits 

 although some of his conclusions have since been modified by other 

 workers. The general results of his investigations may be summarized 

 as follows : 



According to Darton, the Lafayette formation does not end at Fred- 

 ericksburg, but crosses Maryland, Delaware, and Pennsylvania into New 

 Jersey in disconnected areas. In discussing this he said : " The north- 

 ern termination of the deposits was supposed to be near Potomac creek, 

 a few miles north of Fredericksburg ; but I have found that while there 

 is a break in its continuity in the region east of the Potomac river, it soon 

 begins again and thence continues northward probably through Maryland, 

 and in attenuated scattered outcrops, through Delaware and into Penn- 

 sylvania and New Jersey. It is displayed in the high terraces about 

 Washington, and it caps nearly all the higher terrace levels of the 

 " Western shore " of Maryland northward to the latitude of Baltimore. 

 Still farther northward it is confined to outliers on the divides along 

 the western margin of the coastal-plain region; but at the head of 

 Chesapeake Bay it extends farther eastward and, in the high Elkridge, 

 caps the Cretaceous and Potomac formations over a considerable area." ' 



The Lafayette was also described as continuing down the peninsula 

 of the Coastal Plain. In this connection he said : " I have found that 

 the formation extends eastward down the coastal plain peninsulas nearly 

 to Chesapeake Bay. These peninsulas consist of remnants of an elevated 

 plain, occupied by a sheet of Lafayette deposits, and originally con- 

 tinuous over the entire coastal plain. This plain is inclined gently 

 eastward, its altitude decreasing from 500 feet in the Piedmont region, 

 to from 60 to 80 feet in the vicinity of Chesapeake Bay, where it is 



2 Bull. Geol. Soc. Amer., vol. ii, 1891, p. 445. 



