34 The Middle Devoxian Deposits of Makyland 



shales, Hamilton group, Tully limestone, Genesee slate. Portage, Ithaca 

 and Chemung groups,* thus inchiding all the stages of the Middle De- 

 vonian and Upper Devonian of Maryland with the exception of the 

 Catskill, the greater part of which in eastern New York is synchronous 

 with the Chemung and Portage stages/ In the early part of 1842, and 

 perhaps as early as the latter part of 1841,^ Professor James Hall pub- 

 lished a paper entitled " Notes upon the geology of the Western States " * 

 in which he compared the formations of those states with those of New 

 York. He began with the higher rocks, considered the divisions in de- 

 scending order and stated that " The great group of fossiliferous shales so 

 well developed along Cayuga and Seneca lakes, and known as Marcellus, 

 Skaneateles, Ludlowville, and Moscow shales, which, for the sake of 

 brevity, I shall speak of under the name of the Ludloiuville group. This 

 great group, which occupies in New Yoi'k a thickness not less than 

 1000 feet, and contains a greater number of individual fossils than nearly 

 all the other groups, thins out in its western prolongation, losing at the 

 same time its distinctive paleontological character." ' The name, Lud- 

 lowville, however, was preoccupied when used by Professor Hall in 1843 

 for he had already in 1839 applied it to the fissile olive shale on Seneca 

 and Cayuga lakes which he called the Ludlowville shales." 



Ludlowville group, as defined by Professor Hall in 1848 has not been 

 retained for this division of the Devonian system. It agrees with the 

 Hamilton period of Dana as restricted in the last edition of the Manual, 

 except that it did not include the Tully limestone ' and corresponds 

 precisely with the Erian as defined by Clarke and Schuchert." 



' Group was used in the N. Y. reports as equivalent to a formation or lowest 

 stratigraphic division, and not as proposed by the International Congress of 

 Geologists where it is the highest division. 



^Geology New York, Pt. Ill, p. 13. For descriptions of the various stages 

 see pp. 146-195. 



'The signature at the bottom of the page is "Vol. XLII, No. 1, Oct.-Dec, 

 1841." 



* Am. Jour. Sci. & Arts, Vol. xlii, 1842, p. 51. 



^IMd., p. 57. 



"Sd An. Rep., Fourth Geol. Dist. [New York], (Assembly Doc. No. 275, 

 1839), p. 298. 



' Man. of Geology, 4th ed., 1895, pp. 592, 593. 



' Science, N. S., Vol. X, 1899, p. 876. 



