PALEOZOIC TIME — LOWER SILUKIAN. 



497 



no doubt tliat the seas were everywhere well populated. Among the occur- 

 ring fossils in the shales, Graptolites (Figs. 604-609) are often very numer^ 

 ous. The American rocks have afforded a number of Sponges, a few Crinoids 

 and Corals, some Bryozoans, many Brachiopods, few Lamellibranchs, some 

 Pteropods and Gastropods, and a number of Orthocerata and Trilobites. 



Plants. — But little is known of the Seaweeds, as only casts of rounded 

 stems, sometimes simple, often more or less entangled, and consisting of the 

 material of the rock, have been found — and the vegetable nature of these 

 forms is doubted. The coal nodules (page 493) are supposed to have been 

 once in the state of mineral oil, and may have been derived from the decom- 

 position of organic matter of any kind. The hot moisture which consolidated 

 the rock and made the siliceous solution for the associated quartz crystals 

 ■(in which the coal is sometimes enveloped) probably drove the oil from the 

 beds and led to its collection in the cavities or geodes. 



An'imals. — Some of the Sponges were of large size. Fig. 596 represents 

 a specimen (the lower part restored) of a species of Archceoscyphia described 

 by Billings, which attained a length of two or three feet and a diameter of 

 four inches. These Sponges are Hexactinellid in type; that is, have six- 

 rayed siliceous spicules (the rays at right angles with one another). These 



696-598. 



598. 



.*.ft 4 d * d ^ iii, -*J 

 t*v* ■» » c <s^? *p \ 



„*_» ■* ■» W ^ 6 *l 

 •»a ■« » O * fc.% 1 



• 1... ■• K* »>*»•' 



Sponsiozoaus. — rigs. 596, a, Arcliaaoscyphia Minganensis ; 597, Eeceptaculites elegantulus, drawn from a 

 gutta-percha east: 598, E. Calciferus, fragment showing inner surface. Billings. 



species are from the Mingan Islands. Other Hexactinellid Sponges, from 

 Little Metis, Canada, of the genus Protospongia of Salter, are represented 

 in Figs. 599 to 603, natural size. Another species of sac-like form — and 

 rhombic meshes half an inch wide, Palceosaccus Dawsoni of Hinde — had a 

 diameter of 14 inches. They are from the base of the Levis beds, Quebec 

 group, and, according to Dawson, are not newer than the Calciferous. The 

 Eeceptaculites (Figs. 597, 598) are supposed to be Sponges. 



DANE'S MANUAL — 32 



