1887.] NATURAL SCIENCES OF PHILADELPHIA. 395 



A paper entitled "The Miocene Mollusca of the State of New 



Jersey," by Angelo Heilprin, was presented for publication. 



Determination of the Age of Bock Deposits. Prof Heilprin, re- 

 ferring to the methods that had been used by geologists and physi- 

 cists to determine the rate of formation of rock masses, stated that 

 in the case of the organically-formed rocks, especially those, like the 

 chalk, which were largely in the nature of a deep-sea deposit, the 

 data deduced from sedimentation and accumulation were of little or 

 no value, since the rate of growth hei'e was almost wholly depend- 

 ent upon the rate of development of the oceanic organisms which 

 use lime in the construction of their hard parts. In the deposit now 

 accumulating along the sea-bottom, known as the Atlantic or Globi- 

 gerina ooze, the speaker thought we had some direct clue bearing 

 upon the solution of the problem. Manifestly, there can be no more 

 rajiid accumulation of the calcareous ooze than there is lime-carbon- 

 ate suspended in the sea ; and again, the quantity of lime-carbonate 

 (in the form of microscopic tests and fragments) suspended in the 

 sea must depend upon the quantity of the formative material con- 

 tained in the sea the quantity of lime carried in by the rivers. 

 The researches of the officers of the Challenger expedition have shown 

 that in a column of oceanic water of 600 feet depth, with a transverse 

 area of one square mile, there are contained some 16 tons of suspended 

 organic (foraminiferal) particles ; these, if precipitated to the floor 

 of the sea, would make a deposit x^^oo inch in thickness. Now, 

 it would seem from careful observations made on many of the most 

 important rivers of the globe^ that the quantity of lime carried out 

 by them into the sea annually is about one-sixth that of their sus- 

 pended sediment, and would cover the sea-bottom, if precipitated 

 at a rate proportional to that of the removal of continental sediment, 

 one foot in 3000 years to a depth of about :^\o inch. Assuming 

 that one-half of this amount is used by the Foraminifera for the con- 

 struction of their shells, the rest being taken up by the mollusks, 

 corals, etc., then the foraminiferal accumulation from this (ap- 

 parently the only) available source Avould be the ^oVo part of an inch 

 annually, or very nearly the amount that would accumulate from 

 the droppings contained in the 600-foot column of water, as deduced 

 from the Challenger determinations. At this exti-emely slow rate of 

 accumulation, it would require a period of 100000 years to form a 

 single foot, and where, as in the case of the Chalk, we have a similar 

 deposit hundreds of feet in thickness, we would require a period of 

 millions of years for its formation. The speaker stated that there Avere 

 probably factors involved in a more rapid formation of the Atlantic 

 ooze with Avhich we were not acquainted, and it hardly appeared 

 credible to him that the rate of formation could be as slow as the data 

 indicate. But the method of calculation was based upon tangible 

 facts, and was accordingly interesting. 



1 Mellard Reade, Presidential Address, Liverpool Geo). Soc, Oct. 1876. 



