76 THE DEVONIAN AND CARBONIFEROUS. Ibull.80. 



it reposes, and indeed graduates insensibly into that rock, so that the 

 line of separation between them is frequently only an imaginary and 

 arbitrary demarkation." 1 



Thus we see that the Carboniferous as originally understood was 

 grouped about the Coal Measures, had its upper limit a line of uncon- 

 formity, and below had no sharp line of demarkation. 



Murchison and Sedgwick had previously recognized the importance 

 of the Old Red Sandstone as a distinct terrane, and as holding a pe- 

 culiar and interesting fauna, 2 and in 1839, in the Silurian system, Mur- 

 chison raised it to equal rank with the Silurian and Carboniferous, call- 

 ing it the " Old Red system." 



Murchison included in the Carboniferous system the rocks associated 

 with the Coal Measures, which are terminated above by the rocks of the 

 New Red system, and below by those of the Old Red system. The 

 three divisions of the Carboniferous system (Coal Measures, Millstone 

 grit, and Carboniferous limestone) were recognized by Murchison. 



The Old Red system of Murchison included: (1) Quartoze Conglom- 

 erate and sandstone ; (2) Cornstone and marl ; (3) Tilestone. 



Immediately under the Tilestone at Ludlow village was the Upper 

 Ludlow and top of his Silurian system. The Tilestones were regarded 

 as beds of passage to the Silurian. They were afterward called " Down- 

 ton sandstone," a name proposed by John Phillips. 



This was the classification with which the New York geologists sought 

 to correlate the rocks of the New York system in 1840. 



The Carboniferous system was made up of the Coal Measures at the 

 top, the Millstone grit, and at bottom the Carboniferous limestone. 

 Above the Carboniferous came the New Red sandstone or New Red 

 system, in which the Magnesian limestone, the Saliferous group, and 

 the New Red sandstone were conspicuous divisions. Below the Car- 

 boniferous came the Old Red system, which in Murchison's classifica- 

 tion filled the interval between the Carboniferous and Silurian systems. 



The confusion about the Devonian in the final reports of the New 

 York survey arose partly from the original confusion in England. 

 The series in New York are perfectly simple up to the Conglomerate. 

 The Red rocks of the Catskill were identified with the Old Red system. 

 The Devonian rocks were clearly below these Catskill rocks, and while 

 some of their fossils were similar to Phillips's Devonian fossils, others 

 were also like Murchison's Ludlow fossils, and as the Ludlow group im- 

 mediately preceded the typical Old Red rocks of England, and as the 

 chief of Phillips's Devonian fossils were really Upper Devonian, it was 

 natural to conclude that the rocks of our Middle and Lower Devonian 

 were to be correlated with the Ludlow rocks of Murchison. 



The correcting of this mistake could come only from a careful study 

 of the fossils* When this had been done by de Yerneuil the correc- 



1 Op. cit., p. 862. a Geol. Trans., vol. 3. 



