480 HISTORICAL GEOLOGY 



of elevation was followed by one of subsidence and later by disturb- 

 ances which cut off a great lake, like the Caspian Sea, and salt and 

 gypsum were deposited as it dried up. During the Upper Permian 

 the thickest known salt deposits were accumulated, one of which, 

 near Berlin, has been penetrated 4000 feet. 



Permian strata cover large areas in southern Asia, in Australia, 

 in southern Africa, and in South America, the unique features of 

 which are the extensive glacial deposits (p. 505). 



Invertebrates of the Carboniferous 



Protozoans. — During the Carboniferous, for the first time in the 

 Paleozoic, Foraminifera became abundant and varied. Certain genera 



built up limestone 

 deposits, occasionally 

 of considerable thick-' 

 ness. One of the 



m% 



££f&2m*£m, i^fll & most characteristic 



mi I # 



wheat in form and 



fEB*l?3a<£|fc iPiB forms of the Missis- 



tWSw^fc^ 'I MM si PP ian (Fusulina) 



'( I W was like a grain of 



_^j^^S^ im r sIze ( Fi §- 455 H, l 9 



A J p. 482). 



Fig. 451. — Carboniferous corals: A, Lithostrotion CoelenterateS and 



canadense (Mississippian) ; B, Hapsiphyllum calcareforme Echinoderms. — ■ Cup 

 (Mississippian) ; C, Lophophyllum proj 'undum (Pennsyl- /y A-C) ^nd 



vanian). V &• 4b / 



honeycomb corals con- 

 tinued to be important in the Carboniferous, and contributed 

 largely to the formation of thick limestone strata. Blastoids 

 (Fig. 452 F, G) were so abundant in the Mississippian that some 

 beds are largely made up of them, but their extinction was reached 

 before the end of the Pennsylvanian. Where favorable conditions 

 existed, crinoids (Fig. 452 A-E) were unusually abundant; especially 

 was this true in the Mississippian. Sea urchins (echinoids) were 

 more abundant and larger than ever before, but were subordinate 

 to the crinoids in numbers. 



Molluscoids. — Bryozoans lived in considerable numbers. Among 

 many less striking forms was one genus with a peculiar habit of growth 

 about an axis which gave it a screwlike shape, hence the name Archi- 



