502 CLARK AND BIBBINS 
his first report in 1860, led to a much fuller description of the 
Potomac deposits. He recognized two divisions in these basal 
strata, although his descriptions do not make it altogether clear 
that he understood their stratigraphic relations. He, however, 
differentiated the ‘‘Iron-ore Clays” which he described and 
mapped as distinct from another member composed of variegated 
materials (‘‘a thick group of sands and clays of various colors’’). 
He stated that this latter member in places abounded in lignite 
derived from coniferous plants, and in places contained beds of 
ferruginous sandstone. These deposits were referred with the 
sandy clays and greensand above them to the Cretaceous or 
Upper Secondary. In his second report, published in 1862, he 
referred the ‘“‘Iron-ore Clays,’ on the supposed occurrence of 
fossil cycads in the beds, to the ‘‘ Oolitic period.” 
In the “Memoir of the Geological Survey of Delaware,’’* 
published by Professor J. C. Booth, the state geologist of Dela- 
ware, in 1841, the deposits which we are now considering were 
denominated the ‘Red Clay formation,’ and together with the 
‘Greensand formation”’ above them classed as ‘‘ Upper Second- 
ary Deposits.” 
Professor H. D. Rogers, who published reports upon the 
geology of New Jersey in 1836 and 1840, described the deposits 
of that region as ‘‘Clays and Sands” without clearly defin- 
ing their stratigraphic relations. Upon the organization of 
the second Geological Survey of New Jersey in 1854 under the 
direction of Wm. Kitchell, Professor George H. Cook began his 
extended investigations of the Coastal Plain series of that state. 
At a later period, as state geologist, he elaborated and classi- 
fied these deposits in a manner that for many years met with 
wide acceptance. This classification is given in much detail in 
the Geology of New Jersey published in 1868.2 The lowest of 
these formations is described by Professor Cook under the name 
of ‘Plastic Clays” and referred by him to the Cretaceous. 
Little further attempt was made at the investigation of the 
*Mem. Geol. Surv. Del., pp. 38-43. 
* Geology of New Jersey 1868, pp. 249-257. 
