298 PALEOZOIC SYSTEM OF ROCKS. 



The steps of this increase have been carefully studied in New York. 

 The map (Fig. 268) shows the principal successive stejjs, as does also 

 the section (Fig. 264) with which it should be compared. Inspec- 

 tion of these figures shows not only the Silurian bordering the Lau- 

 rentian, but the rocks of the several periods bordering each other 

 successively ; so that in walking from Pennsylvania to Canada, or to 

 the Adirondack Mountains of New York, we successively walk over the 

 Carboniferous, the Devonian, the Silurian, and the Laurentian ; and 

 in the Silurian over rocks of the successive periods, from the highest 

 to the lowest. This plainly shows that during Silurian times the con- 

 tinent (Laurentian area) was slowly upheaved, and contiguous sea-bot- 

 toms successively added to the land, and the shore-line gradually pushed 

 southward from the Canadian region, and probably westward from the 

 land-mass along the Appalachian. Of course, therefore, the oldest 

 Silurian shore-line was the most northern and eastern. This is the 

 primordial beach. 



Primordial Beach and its Fossils. — As already stated, the element- 

 ary character of this treatise renders it impossible to take up separately 

 the several periods of this age. We must confine ourselves to a general 

 description of the age only. But there is so peculiar and special au 

 interest connected with the dawn of life on the earth, that, before taking 

 up the life-system of the whole age, it seems necessary to say something 

 of the earliest fauna. 



We have seen that at the beginning of Silurian times a large V- 

 shaped mass of land occupied the region now embraced by Canada and 

 Labrador, and stretched northwestward to an unknown distance, the two 

 arms of the V being nearly parallel to the two present shores of the 

 American Continent; further, that a land-mass of extent unknown 

 occupied the position of the eastern slope of the Appalachian chain ; 

 also, that land of unknown extent occupied the position of the Rocky 

 Mountains and Basin region ; and the continent was thus early sketched 

 out. Now, southward of the first-mentioned land-area and between the 

 other two there was a great interior sea, which we have called the In- 

 terior Palaeozoic Sea. The shores of that sea beat upon the continental 

 masses north, east, and west, and accumulated, on exposed places, a 

 beach. Patches of that earliest beach still remain. They are found, 

 of course, closely bordering the Laurentian rocks, Canadian and Appa- 

 lachian, and lying unconformably upon them. They are the primordial 

 sandstones and slates of Canada, New York, Pennsylvania, Virginia, 

 and probably Tennessee and Georgia, The fact that these are indeed 

 remnants of a beach is proved by the existence, in almost every part, 

 of shore-marks of all kinds — such as ripple-marks, sun-cracks, worm- 

 tracks, worm -borings, broken shells, etc. 



This, then, is the old primordial beach. It is of the extremest inter- 



