[7] THE BOTTOM OF THE GULF STREAM. 1051 



the shells of foraniiulfcra abuudaiitly disseminated throngh the sand, 

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

 cases I was able to identify distinct casts of foraminifera in the rock. In 

 some pierces 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 pick them u}). The age 

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

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

 belong to a i)art of the same formation as the masses of fossiliferons 

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

 cester tishermen from deep water on all the tisliing banks fi'om George's 

 to the Grand Bank. ]SIo rocks of this kind are found on the dry land of 

 this coast. 



The chemical composition of these limestone nodules is of much inter- 

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

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

 garded as magnesian liaiestones or dolomites of recent submarine origin. 

 They also contain a notable quantity of calcium pJiosphafe. 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 Uchini, Holothnrians, 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 DRKP-SEA LIMESTONE. 



(Specific gravity, 2.73.) 



Lime '. 24. 95 



Magnesia 14. 41 



Iroii, estiiiiafed as protoxide 2. 00 



Insoluble residue Ki. 97 



Throughout the Gulf Stream Slope examined by us the bottom, in 70 

 to 300 fathoms, 60 to 120 miles from the shoro, is composed mainly of 

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

 etc. With it there is always a (;onsiderable percentage of shells of for- 

 aminifera and other calcareous organisms, and also spheri(;al, 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 



