300 C. SCHUCHERT MEDIXA AXD CATARACT FORMATIONS 



five hundred feet in thickness developed, we find no more than forty feet 

 of a siliceous character. . . . The marl in tlie lower part of the for- 

 mation is striped, vertically and horizontally, with seams of green shale/' 

 It is therefore seen that Hall here follows the example of Eaton . and 

 Conrad in including the marl (^ Queenston) and the higher sandstones 

 (= Medina) all in one formation, a correlation that was continued until 

 1905. 



"At Medina, about forty feet from the top of this rock, we find a 

 stratum, two feet tliick, of siliceous sandstone of a greenish gray colour, 

 containing LinguJa, Cyclostoma, Planorbxs, Unio and Cytherina. . . . 

 The points at which this formation can be most advantageously exam- 

 ined, are along the Genesee Eiver, below Rochester, at Medina, Orleans 

 County, and along the Xiagara River, near Lewiston." 



We now come to Hal?s Third Annual Report (1839), important be- 

 cause it is here for the first time that the principle is defined as to how 

 formations shall be named. The use of a geographic name of the locality 

 where the formation is typically developed was not new with Hall; but 

 to him we must give the credit in that he was the first American to see 

 clearly what must be done in this matter and to act accordingly, so that 

 stratigraphers thereafter might become more certain of what they de- 

 scribed. 



Hall relates that he traveled with his colleague, Vanuxem, for "several 

 weeks in examination along the boundary line between the Third and 

 Fourth Districts." Vanuxem, learned and conservative, a graduate of 

 the School of Mines in Paris, had great infiuence over Hall, as the latter 

 related to the writer in 1889. Undoubtedly the principle of a type local- 

 ity was formulated by Hall during this association in the summer of 

 1838, and in his report of 1839 many of our formation names now in 

 use take their origin. He says : 



"Hereafter we shall be enabled to avoid collision and discrepancy in 

 our descriptions, and to designate groups without confounding them 

 with each other. We have also found the solution of many difficulties, 

 in part arising from previous partial examinations, and also from the 

 fact that the character of several rocks below the Onondaga limestone 

 entirely or materially change in their eastern prolongation; and more 

 especially after passing the longitude of Cayuga Lake. . . . 



"Every one who has studied rocks even partially, is aware of the in- 

 sufficiency of mineral or lithological characters for giving nomenclature, 

 and the many errors into which he may be led, whether in his own re- 

 searches or by the mistakes of others. So likewise in the present state 

 of our knowledge, we ^re unable in all cases to give names from fossil 



