456 PRINCIPLES OF STRATIGRAPHY 



genera and 35 species of planktonic pteropods in this ooze, but only- 

 three genera, Limacina, Clio and Cavolinia, are abundantly repre- 

 sented. With these occur the heteropods Carinaria, Atlanta and 

 Oxygyrus. These shells make up from one-quarter to one-half the 

 entire mass, the remainder being chiefly Foraminifera. The depth at 

 which these delicate shells occur is between 1,000 and 2,700 meters; 

 below this they give way to purer Globigerina ooze. In the Atlantic 

 these deposits occur especially around the Azores, on the outside 

 of the Antilles, west of the Canary Islands, and on the South At- 

 lantic rise between Ascension and Tristan da Cunha. In the Indian 

 Ocean they occur off the African coast from the equator to Soko- 

 tora, and to the west of Cape Comorin near the Nicobar and Men- 

 tawie Islands. In the Pacific they surround the Fiji Islands, occur 

 east of the Great Barrier Reef, around the Kermadec and Hawaiian 

 Islands, and especially in the region of the Paumota or Low Archi- 

 pelago. The total area covered by these deposits does not exceed 

 one and a half million square kilometers. 



Fossil Ptcropod Oo::es. These are known from various hori- 

 zons ; in the Upper Devonic of New York State occurs a lime- 

 stone composed almost entirely of Styliolina iissurella, embedded in 

 dark shales, which are sparingly or not at all fossiliferous. The 

 limestone varies in thickness from 6 inches to a few feet, and has 

 been traced from the Genesee Valley to Lake Erie, a distance of 

 over sixty miles. Clarke has estimated that 40,000 individuals oc- 

 cur on the average in a cubic inch of the rock ( 16 '.13). In the Cam- 

 bric, beds of limestones, largely composed of Hyolithes and Ortho- 

 theca, occur, and some Upper Siluric horizons carry layers formed 

 of Tentaculite shells (Manlius limestone of New York, etc.). 



Entomostracan Ooaes. These are seldom of great purity as 

 oceanic deposits. The Ostracoda, Crithe and Cythere are abun- 

 dant among the plankton of the ocean, and their shells are found 

 mingled with Foraminifera and pteropods. No pure marine ostra- 

 cod ooze has been obtained from the deep sea. These organisms 

 also occur in salt pools (Cypris salina, etc.), in the estuaries of 

 rivers (Cypris, Potamocypris, Pontocypris, Cythere, etc.) and in 

 fresh-water lakes and pools. At the Ayin Musa Springs near Suez, 

 calcareous deposits are formed by the abundant accumulation of 

 the shells of Cypris delecta (Fraas-32 : 182). Limestones of Cypris 

 shells have also been found in the fresh-water Tertiary deposits of 

 western America. Eolian deposits of this type are also known. 



Coc eolith and Rhabdolith Oozes. Coccoliths are the minute 

 oval plates of lime which cover the planktonic Coccolithophora, 

 small algse of the order Calcocytea, while rhabdoliths are slender 



