260 PALAEOZOIC TIME — UPPER SILURIAN. 



included frigid winds or seas. The living species in the waters 

 between the parallels of 30° and 45° were in part the same, or 

 closely related in species, with those that nourished between the 

 parallels of 65° and 80°. (See pages 238 and 242.) From this life- 

 thermometer we learn only of warm or temperate seas. 



FOEEIGN UPPEB SILUKIAK 



The rocks of the Upper Silurian are widely distributed over the 

 globe, though less universal than those of the lower Silurian. They 

 occur in Great Britain, Scandinavia, Kussia, Germany, Sardinia, and 

 Bohemia, but have not been identified in France or Spain : also in 

 Asia, Africa, and Australia. Throughout, they sustain the prin- 

 ciple that the earlier formations are in general of continental 

 range. They seem on a geological map to cover but small areas, 

 but only because they are concealed by later formations : they lie 

 underneath. 



The table on page 168 exhibits some of the foreign equivalents of the Ameri- 

 can Upper Silurian. 



The equivalents of the Niagara period in Great Britain are (1) the Lower 

 Llandovery beds of South "Wales (especially near Llandovery), supposed to 

 correspond to the Medina group; (2) the Upper Llandovery of Shropshire and 

 other localities (including the May Hill sandstone), corresponding to the Clinton 

 group ; (3) the Wenlock group (divided into the Lower Wenlock or Woolhope 

 limestone, the Wenlock shale, and the Upper Wenlock or Dudley limestone), 

 corresponding to the Niagara limestone. The Ludlow group (4) (consisting of 

 the Lower Ludlow rocks, the Aymestry limestone and the Upper Ludlow) is re- 

 garded as corresponding to the Lower Helderberg. 



The largest Upper Silurian area in Great Britain is situated near the borders 

 of Wales and England, where are the May Hill sandstones, the Wenlock or Dud- 

 ley limestone and shales, and the Ludlow argillaceous sandstones and shales, in 

 which lies the Aymestry limestone. Another area is in northern England, on 

 the west side, where are the Coniston grits, the Ireleth slates equivalent of the 

 Wenlock, and the Kendal tilestones equivalents of the Upper Ludlow. There are 

 other areas in southern Scotland and Ireland. The thickness of the British Upper 

 Silurian is about 5000 feet.* 



In Scandinavia, the limestones and sandstones of Gothland represent the 

 Niagara, and the Calciferous flags and Upper Malmo group the Upper Helder- 

 berg. In Bohemia, the Upper Silurian rocks are limestones and schists of Bar- 

 rande's formations E, F, G, H. 



* The student desiring information on the Silurian of England will find the 

 subject displayed with great fulness in Murchison's Siluria, the second edition of 

 which appeared in England in 1859. The work also gives the best digest that 

 has been made of the facts relating to the Silurian and other Palaeozoic formations 

 of Europe. 



