LOWER SILURIAN. 181 



In the next or Potsdam epoch, there were beach deposits of sand in 

 progress about the shores of the Archaean dry land, but in Vermont 

 mostly shales, with some limestones, indicating deeper waters off the 

 Archaean coasts. West of Vermont, this coast line bent around the 

 Adirondack region of northern New York and Canada, as marked 

 out by the distribution of the Potsdam. The Potsdam rocks of New 

 York and Canada indicate their beach or shallow-water origin, by their 

 foot-prints, worm-borings, ripple-marks and mud-cracks (p. 169). Simi- 

 lar evidences of shallow water are observed also in the Potsdam rocks 

 of Pennsylvania and Tennessee. Thus we are enabled to run a line 

 of soundings along the continental sea of the Potsdam era. The ma- 

 terials of the sandstones were the moving sands and pebbles of the 

 shores and shallow seas; and the animals which had living places over 

 these flats and sea bottoms found in them also a burial place, to remain 

 as fossils and become testimony as to the early life of the world. 



2. Climate. — No marked difference between the life of the Pri- 

 mordial period in warm and cold latitudes has been observed ; and 

 there is wanting, therefore, all evidence of a diversity of climate and 

 of oceanic temperature over the earth's surface. With a warm and 

 equable climate, the atmosphere would have been moist and the skies 

 much clouded ; but storms would have been less frequent or violent 

 than now. The eyes of the Trilobite, as Buckland observes, indicate 

 that there was the full light of day, and therefore that sunshine alter- 

 nated with the clouds as now. 



So far as has been deciphered in the history of the Primordial 

 period, there was no green herbage over the exposed hills; and no 

 sounds were in the air save those of lifeless nature, — the moving 

 waters, the tempest and the earthquake. 



3. Exterminations of life. — The life of the Primordial period 

 changed much during its course ; and, at one time — the close of the 

 Acadian epoch — there was a general extermination of the species 

 about the eastern portion of the continent ; for no species of this epoch 

 have yet been found in the higher rocks. Among the Trilobites, the 

 genus Paradoxides, some of whose species were the largest of known 

 Crustaceans, became extinct ; most of the other genera remained, but 

 were represented by new species. No Trilobites of the Primordial 

 extend up, so far as known, into the beds of the next period. 



V. Disturbances during the progress of the Primordial period. 



In Newfoundland, the beds of the Potsdam division lie unconform- 

 ably over those of the Acadian, indicating an epoch of disturbance 

 between. No direct evidence of a similar disturbance over the rest of 

 North America has yet been made known, beyond the fact of the de- 



