378 THE 0RD0V1CIAN PERIOD 



continent. In Nova Scotia and New Brunswick the Silurian 

 strata lie unconformably upon the upturned Ordovician. Along 

 the line between New York and New England the Taconic range 

 was upheaved, its rocks greatly compressed, plicated, faulted, and 

 metamorphosed. Many of the crystalline schists of this region, it 

 has been proved, were derived from the metamorphosis of Cam- 

 brian and Ordovician sedimentary rocks. Evidences of this dis- 

 turbance have been traced as far south as Virginia. The effects 

 of the upheaval were not felt in the northern part of the Gulf of 

 St. Lawrence, for on Anticosti Island the great limestone, which 

 was begun in Ordovician times, continued without a break into 

 the Silurian. The disturbance was along a line of especially thick 

 accumulations, as appears from the comparative measurements of 

 the same strata in different areas. Westward over the Interior 

 Sea, the upheaval was, for the most part, of slight amount, so that 

 in this region there are no very marked unconformities between 

 the Ordovician and the overlying Silurian. Some narrow strips 

 of land were added to the margin of the Cambrian coasts, and on 

 a line running through southern Ohio, Kentucky, and Tennessee 

 a low, broad arch was forced up by lateral compression. This 

 is called the " Cincinnati anticline." 



In Europe the disturbances which brought the Ordovician to a 

 close produced their maximum effects in England, Wales, and the 

 Highlands of Scotland, where the thickness of the sediments is 

 greatest. In these regions the Ordovician beds are folded and 

 often greatly metamorphosed, the Silurian strata lying upon their 

 upturned edges. 



The Life of the Ordovician 



Ordovician life displays a notable advance over that of the 

 Cambrian, becoming not only very much more varied and luxu- 

 riant, but also of a distinctly higher grade. During the long ages 

 of the period also very decided progress was made, and when 

 the Ordovician came to its close, all of the great types of marine 

 invertebrates and most of their more important subdivisions had 

 come into existence. In a general way the life of the Ordovician 



