The term "passive" is used to indicate that this margin lies within the bounderies of one of the great plates which make up the earth's crust and responds to relatively simple geologic processes in the course of its evolution. The goal of investigating the passive continental margins is to understand the early history of formation and opening of an ocean basin. Most geologists believe that the continent broke apart by a process which first involved arching and stretching with the result that a rift valley formed on the continental surface. The modern analog is the East African Rift Valley which contains great, deep fresh water lakes, such as Lake Tanganyika and the headwaters of the Nile and Congo Rivers. Because of the climatological conditions which would have existed at the time, we expect that the lakes that formed on the site of the future Atlantic Ocean were stagnant, with bottom sediments rich in organic carbon, and that these sediments accumulated to thicknesses in the order of several thousands of feet. As the continent stretched further and began to be pulled apart, the (Figure 3. rift valley sank below sea level. The Dead Sea area is a modern example of this process. The narrow seaway became the site of salt deposits which would overlie the deeper lake sediments.

(Figure 2.)

As the continental fragments pulled further apart, true basaltic ocean crust began to appear and with an opening to the ocean, salt deposition ceased. Great barrier reefs developed and grew (Figure 1) along the sides of the ocean opening, only to die out abruptly and become buried beneath detritus washed in from land. (Figure 5.

5.)