588 GEOLOGY 



northwestern province, as also to the interior province after the 

 latter had been invaded by the Onondagan and Northwestern 

 Hamilton faunas. While its fauna is not yet known well enough 

 to permit final conclusions, it bids fair to offer a fine example of a 

 steady, uninterrupted development of a provincial fauna. 



II. The Life of the Land Waters 



Principle of interpretation. For geological purposes, all fishes 

 that lived in streams and lakes, and those of the freshened waters 

 of the estuaries, bays, and inlets on the land border, may be classed 

 as fishes of the land waters. But there is difficulty in some cases 

 in determining which sedimentary formations were made on the 

 land or in land waters, for terrestrial, marine, fluviatile and estu- 

 arine types of life may be mingled by the carriage of land forms to 

 the sea. Fossils do not always tell us, therefore, whether a forma- 

 tion was made in the sea or on land. The deposits forming to-day 

 in the great valley of California embrace pluvial, fluvial, lacustrine, 

 and marine deposits. At a geologically distant day, only small 

 parts of this aggregate would probably be fossiliferous, and the 

 evidence from various points might be quite opposed. This appears 

 to be very much the state of things recorded in the "Old Red Sand- 

 stone," in the Catskill formation, and elsewhere. As all these 

 deposits were laid down in more or less local basins, probably, their 

 exact correlation is impossible, and their faunas may be considered 

 together. The general faunal conception is that in the Appalachian 

 tract and in the Canadian provinces lying to the northeast of it, 

 as well as in Great Britain and Russia, there were many lodgment 

 basins that were progressively filled by land-wash and fresh-water 

 sediments, and that these basins were the home of a fresh- or 

 brackish-water fauna, of which ostracoderms, fishes, and crusta- 

 ceans were the most conspicuous members. Perhaps the geo- 

 logical record presents no more suggestive combination of ancient 

 life. The type of the fauna was foreshadowed by the eurypterids 

 and fishes, or fish-like forms of the late Silurian; but the record 

 of that time is more imperfect than that of the late Devonian. 



The ostracoderms. The center of interest in this fauna is 

 found in the ostracoderms (Figs. 420 and 421), which were first 



