426 Reviews — Pourtales on the bed of the Gulf-stream, 



Crisfellarice. In the fifth zone, in depths of 60 fathoms and upwards, 

 the sand is very much mixed with GloMgerince, which in depths of 

 100 fathoms become so frequent that they actually form the entire 

 mass. This continuation of zones shows the same character as far 

 down as Cape Florida. Limestone of Tertiary age occurs only at a 

 few places, forming small banks and clifis, affording a suitable 

 habitat to species of corals. The neighbourhoods of these banks 

 are generally richer in fishes. But the small islands between Cape 

 Florida and Cape Sable are all formed by coral limestone ; the 

 siliceous bottom which begins at the latter point is there much mixed 

 with lime from the coral banks. 



It is remarkable to observe how the littoral fauna changes with 

 the condition of the sea-bottom. Many forms common to the coast 

 of Carolina disappear at Cape Florida, and reappear at Cape Sable, 

 as, for instance, the oysters, which at Florida are driven away by the 

 West Indian Coral-fauna. The mud-bottom contains only few 

 Guttulince (Polymorphinai) , whilst the lime-bottom is exclusively of 

 organic origin, consisting either of Corals or of Polythalamice. 

 Cape Florida is the most northerly point to which corals extend ; 

 the coral reef there does not show the same steep incline as the 

 coral islands of the Pacific, or like the Bahama islands close by. 

 Between this reef and the depth of about 100 fathoms, the bottom 

 consists only of remains of shells, pieces of corals and such like, 

 showing rolled edges. The following semicircular region, inclosing 

 the former, called the plateau of Pourtales, gradually deepens to 

 about 300 fathoms ; it consists of a hard, dark-brown limestone, 

 whose surface is animated with corals and a large fauna of all classes 

 of Invertebrata, Crustacea, Mollusca (two Brachiopoda and Valuta 

 Junonia), Echinoderma, Ophiura, Asteria, Holomacea. The sea- 

 bottom near Cuba is also similar, but forms a steep inclination, which 

 (at 400 fathoms) bears a fauna totally different from that near 

 Florida, The steep banks of Bahama are covered with soft white 

 lime mud. The lime-bottom, which consists almost entirely of 

 Polythalamia, covers in greater dej)ths the entire channel of Florida. 

 This formation extends without interruption over the whole bed of 

 the Grulf-stream in the Gulf of Mexico, is continued along the 

 Atlantic coast of America, and most probably also extends over the 

 greater part of the Atlantic basin. The commonest genera met with 

 in this deposit are Glohigerina, Botalia cultrata, in large numbers, 

 several Textilarice, MarginuUncs, etc., etc. Besides these, small free 

 corals, Alcynoidce, Opliiurce, Mollusca, Crustacea, small fishes, etc., 

 etc., are found living in these depths. Bhizocrinus lofotensis was 

 often met with, and was also found near the coasts of Norway, 

 Great Britain, and the Azores, always within the reach of the Gulf- 

 stream. The whole sea-bottom appears to be covered with a vast 

 deposit of white chalk still in formation, whilst in the littoral and 

 deep-sea region, the corals and shells of mollusca afford material 

 for Oolite coral limestone and conglomerates. 



Between Georgia and South Carolina, in depths of from 50 to 100 

 fathoms, almost at the line of demarcation of the siliceous and lime 



