NORTH AMERICAN GEOLOGY. 193 



stratified beds comi">osing the greater mass of tlie formations of the 

 island are unconformably overlain by the drift, but although they yield 

 some fossils, their age is considered uncertain. Some of the clays ex- 

 posed along the north shore may be Cretaceous, and other clays and 

 sands are thought to be Tertiary, while the greater mass of the strati- 

 fied sands and gravels are thought to represent the Post-pliocene of 

 Sankaty Head and Gardiner's Island.* 



11. The same author reports the preliminary results of a detailed study 

 of the Quaternary and recent formation of the coast region of New Jer- 

 sey, made under the direction of the State geologist. Professor Cook.t 

 An account is given of the subsidence of the coast and the variations in 

 its rate. It is found also that the ocean shore is wearing away and the 

 winds and waves cause its recession westward. Beach and strand 

 formation is discussed, and descriptions are given of the several beaches 

 and their recent changes. 



12. In the introduction to this report | Professor Cook discusses the 

 terraces of the coastal plain. They occur from 40 to 60 feet above tide, 

 and it has been determined that they slope southward at the rate of 

 three inches to the mile. It is thought that the higher terraces mark 

 the position of the ocean level at the close of the glacial period, and 

 that there has been an uplift between that time and the present subsi- 

 dence. 



13. On the northeastern corner of Staten Island Britton finds the 

 morainal beds capping the finely stratified sands and clays along a line 

 of contact between 25 and 30 feet above tide, indicating at least that 

 amount of elevation since the glacial period, but there are other de- 

 posits of pre-glacial drift of much greater elevation on the island, and 

 some other areas have been recently discovered. § 



14. In a paper on the geology of Washington and vicinity, McGee 

 gives an account of the Quaternary formations of that district. The city 

 lies on the terraces of an amphitheater extending back from the Poto- 

 mac. Up to an elevation of about 100 feet there is found a well-defined 

 Quaternar}^ deposit to which the name Columbia formation is applied. 

 Its upper portion consists of loam or brick clay, varying from nothing to 

 20 or 30 feet in thickness; and its lower, of sand, gravel, and bowlder 

 beds, from a trifle to 20 feet in thickness, all more or less stratified 

 throughout. It is thought that it represents a subaqueous delta of the 

 Potomac River, deposited during the period of formation of the terraces. 

 Its absence from above tide on the eastern side of the amphitheater is 

 attributed to a dislocation bounding the coastal plain, of which other 

 evidence is also found. || 



* New York Acad. Sci. Annals, vol. 3, pp. 341-364. 



tNew Jersey Geological Survey, Annual Report of the State geologist for 1885, pp. 

 61-9.5. 



( lb., pp. 5.5-61. 



^ Nat. Ilist. Soc. of Staten Island, Proc. April, I88f). 



II District of Columbia, Report of the Health Officer for 1885, pp. l'.»-21, 23, 24, 25; 

 Am Joui., Sci. Ill, vol. 31, pp. 473-474. 



H. Mis. 600 13 



