260 PALEOZOIC TIME — UPPER SILURIAN. 



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. 



FOREIGN UPPER SILURIAN. 



The rocks of the Upper Silurian are as widely distributed over 

 the globe as those of the Lower Silurian, occurring in Great Britain, 

 Spain, France, Germany, Russia, Sardinia, and other countries of 

 Europe, and in Asia, Africa, and Australia. Throughout, they sus- 

 tain the principle that these early formations are in general of con- 

 tinental 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 

 regarded 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 Dudley 

 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 limestones and 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 thick- 

 ness 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 Medina and Clinton epochs are represented mainly by 

 sandstones or quartzites, and the later Upper Silurian by limestones and schists 

 of Barrande'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. 



