THE ORDOVICIAN PERIOD. 307 



where the Appalachian mountain system was to appear later, lime- 

 stone, the product of clear waters, is very subordinate to clastic rocks 

 among the formations of the Ordovician system. Concerning the 

 formations made along the eastern border of Appalachia, little is 

 known. If the Ordovician shore was east of the present coast, the 

 formations of the period are obviously not exposed; if it was west 

 of the present coast, the sediments deposited within the present land 

 area were either subsequently removed by erosion, or are concealed 

 by later beds, or have been metamorphosed, for the most part, past 

 recognition. 



The beds of sediments forming at the same time in Newfoundland 

 and in the northeastern parts of Canada were largely of limestone, 

 indicating that abundant debris from the land was not brought to 

 this region. Likewise in the area west of the Adirondacks, in the 

 Ottawa basin, the prevailing sedimentation seems to have been organic 

 rather than clastic, indicating that the land to the north was not fur- 

 nishing abundant sediments to this region, either because it was low, 

 or perhaps well clothed with vegetation, or because the drainage was 

 in some other direction. 



About the isolated land masses farther west, beds of sand and mud, 

 subsequently to become sandstone and shale, were in process of accu- 

 mulation; but the sources of material appropriate for such formations 

 were not extensive, and the formations themselves are correspondingly 

 limited. Here the conditions for the formation of limestone prevailed, 

 for while shell-bearing and other lime-secreting animals and plants 

 may have been no more abundant far from land than near it, their 

 shells were probably more abundant relative to the sediments derived 

 from the land. The occasional variations from limestone to shale or 

 sandstone in this region were probably connected with oscillatory 

 relations of land and sea, or currents. When the land was low, and 

 the waters relatively free from terrigenous sediments, limestone appears 

 to have been making; when the land was higher, more material was 

 brought to the sea by the streams; and where the ocean water was 

 shallow, this material was carried relatively far from the land whence 

 it came. 



But even during those intervals when the land was so low as not 

 to yield abundant sediments, preparation was making for future for- 

 mations of clastic rock. While in this attitude, the formations of the 



