[7] THE BOTTOM OF THE GULF STREAM. lOf)! 



the shells of foraiuinifcra abimdantly disseminated through the saud, 

 just as we find the recent foraminifera, in the same region. In some 

 cases I was al)le to identify distinct casts of foraminifera in the rock. In 

 some pieces of the rock distinct fossil shells were found, ap])arently of 

 recent species {Astarte, etc.). 



The larger masses appear to have been originally concretions in a 

 softer deposit, which has been more or less worn away, leaving the 

 hard nodules so exposed that the trawl could ])ick them up. The age 

 of these rocks may, however, be as great as the pleistocene, or even tlie 

 pliocene, so far as the evidence goes. Moreover, it is probable that they 

 belong to a part of the same formation as the masses of fossiliferons 

 sandv limestone and calcareous sandstone often brought up by the Glou- 

 cester hshermen from deep water on all the fishing banks from George's 

 to the Grand Bank. No rocks of this kind are found on the dry land of 

 this coast. 



The chemical comi)osition of these bmestone nodules is of much inter- 

 est geologically. Analyses made hy Prof. O. D. Allen prove that they 

 contain a considerable amount of magnesia. They are, therefore, to be re- 

 garded as magnesian limestoues or dolomites of recent submarine origin. 

 Tliey also contain a notable quantity of calcium pliosphafe. The presence 

 of the latter is not surprising, when we consider the immense number 

 of carnivorous fishes, Cephalopods, etc., which inhabit these waters, and 

 feed largely upon the smaller fishes, whose comminuted bones must, in 

 part at least, be discharged in their excrements. In fact, it is probable 

 that the greater part of all the mud and sand that covers these bottoms 

 has passed more than once through the intestinal canals of living ani- 

 mals. The Echini, Holothiiriuns, and many of the star-fishes and worms 

 continually swallow large quantities of mud and sand for the sake of 

 the minute organisms contained in it, and from which they derive their 

 sustenance. 



The following partial analysis of one of the limestone nodules is by 

 Prof. O. D. Allen, of the Sheffield Scientific School : 



ANALYSIS OF DEEP-SEA LIMESTONE. 



(Specific gravity, 2.73.) 



Lime 24.95 



Magnesia 14.41 



In)u, estimated as protoxide 2. 00 



Insoluble residue 16. 97 



Ti.roughout the Gulf Stream Slope examined by us the bottom, in 70 

 to 300 fathoms, GO to 120 miles from the shore, is composed mainly of 

 very fine sand, largely quartz, with grains of feldspar, mica, magnetite, 

 etc. With it there is always a considerable percentage of shells of for- 

 aminifera and other calcareous organisms, and also spherical, rod-like, 

 and stellate, sand-covered rhizopods, often in large quantities. In the 

 deeper localities there is usually more or less genuine mud or clay, but 



