SUMMARY OF RESULTS. 
99 
formation occurs without interruption along the bed of the Gulf Stream, in the sinuosities 
of the Gulf of Mexico, and in the deep channels through the Bahama Bank, and again 
along the Atlantic coast from a depth of 100 fathoms, or, what comes to much the same 
thing, from the internal edge of the Gulf Stream, whence it stretches over a vast extent 
of the Atlantic. He says the whole bottom is an immense bed of chalk in process of 
formation, while the littoral fauna, with its numerous Corals and Molluscs, will furnish 
material for oolitic calcareous beds of shells, corals, conglomerate, &c. 
Pourtales also gives a description of the different stages in the formation of glauconite. Pourtales on 
He says : — “ We find, side by side, the tests perfectly fresh, others still entire, but filled ® TAGES IN rjE 
with a rusty-coloured mass, which permeates the finest canals of the shells like an Greensand. 
injection. In others, again, the shell is partly broken away, and the filling is turning 
greenish ; and finally we find the cast without trace of shell, sometimes perfectly 
reproducing the internal form of the chambers ; sometimes, particularly in the larger 
ones, cracks of the surface or conglomeration with other grains obliterates all the 
characters. They even coalesce into pebbles, in which the casts can only be recognised 
after grinding and polishing.” 1 Pourtales observes that these glauconitic grains are 
deposited in depths of 50 to 100 fathoms near the coasts of Georgia and South Carolina. 
Greensand may also be found in the bed of the Gulf Stream, but in such cases it is 
sporadic! Dredgings were taken down to a depth of about 700 fathoms, the zoological 
results of which were published by the Museum of Comparative Zoology, Cambridge, 
Massachusetts. In 1869 L. Agassiz addressed to Professor Pierce a report bearing upon 
the general results of these dredgings, 2 showing how instructive they were in account- 
ing for the manner in which certain geological strata have been deposited in the 
ocean. The Corals dredged from the Pourtales Plateau have some affinity with Tertiary 
and Cretaceous types, while the Echinoderms have some resemblance to those of the 
chalk ; Voluta junonia, also found there, is related to Voluta lamberti of the Crag and 
Voluta mirabilis of the Miocene strata of Virginia and Maryland. Two common 
Brachiopods contribute to give the fauna an archaic character. Beyond this plateau the 
bottom descends rapidly to 500 or 600, and even 800, fathoms, and is covered with a 
thick adhesive mud presenting the aspect of a Cretaceous marl ; s life here diminishes, 
which he thinks is due to the very nature of the bottom. 
Agassiz is of opinion that the exploration of the sea must prove of advantage to the Louis Agassiz on 
study of geology, and states that what he had seen of deep-sea deposits seemed to qf^ont^^ts 
indicate that no recent or ancient formation ever occurred in very deep water. He and Oceans. 
concludes that the present continental areas within the 200-fathom line, as well as the 
oceans, have preserved their outlines and positions from the earliest times. 5 The 
1 Report U.S. Coast Survey for 1869, p. 224. 
s Report upon deep-sea dredgings in the Gulf Stream during the third cruise of the U.S.S. “Bibb, Bull. Mu-'. 
Comp. ZooL, vol. i. pp. 363-386, 1869. 3 Ibid., p. 367. 4 Ibid., pp. 368, 369. 
