538 C. SCHUCHERT SILURIAN FORMATIONS 



mined line, is the break to be discerned. It is this state of affairs that 

 has perplexed and still perplexes stratigraphers. 



At Eondout, New York, there is no Salina present, and 8 miles to the 

 southwest there is from 80 to 90 feet of it. Following along the strike 

 of the mountains, the formation thickens rapidly; so that at Otisville 

 there is at least 800 feet, at the Delaware Gap 2,425 feet, at the Lehigh 

 Gap 2,500, and at the Schuylkill Gap there may be 3,000 feet. In all of 

 these places the deposits are more sandy, while farther west and away 

 from the shore the Salina thins and becomes more and more calcareous 

 to the southwest. In Jacks Mountain the thickness is 1,930 feet, at 

 Tyrone 1,350 feet, and west of Cumberland, Maryland, it is 1,300 feet; 

 the last place is about 300 miles to the southwest of Eondout. 



The origin of the red color of the Salinan shales is usually ascribed to 

 the time of deposition and is thought to be due to periodic subaerial 

 oxidation under a dry climate — vast marine flats that were periodically 

 dried out and sun-cracked, reducing the iron in the sandy shales to the 

 ferric condition. It would seem that this must be the genesis for all the 

 deep red and maroon or brick-colored shales; but as for the lighter reel 

 and pinkish shales, some at least owe their color to recent weathering and 

 the percolating subaerial waters. Proof for the latter mode of red color 

 origin is brought forward by Brown, 17 who says that the red color of the 

 High Falls shale "is not an original character, but has been produced by 

 comparatively recent weathering, and practically fails where these beds 

 are uncovered away from the outcrop or the effects of circulating ground 

 waters." In the deeper parts of the shafts and tunnel of the Eondout 

 Valley the High Falls shales are green or black in color. Brown's ex- 

 planation, however, can not be applied everywhere, and especially not to 

 the brick-red shales of the Salinan series of Pennsylvania. 



The fossils of the Salinan series do not occur in the reel beds, but only 

 iu the yellow and blue more or less calcareous shales or in the water! imes. 

 In most cases the organisms are ostracods of small and large species. 

 The smaller ones often abound in countless numbers and are mainly of 

 undescribed species of the genera Kloedenia and Klcedeniella. The larger 

 forms all appear to be Leperditia altoides and L. alta, which range 

 throughout the Cayugan, and the latter even high into the Lower Devo- 

 nian. On the other hand, the Clinton species are very different forms, 

 the commonest ones being Beyrichia lata (a guide fossil) and the less 

 ornate and smaller Bollia lata. In another year the Maryland Geological 

 Survey will have published a monograph on the Silurian of that State, 

 and in this the above-mentioned Ostracoda, along with the new forms, 

 will be described and illustrated by Ulrich and Bassler. 



"Op. clt., p. 474. 



