1 8 NEW YORK STATE MUSEUM 



Each of these time divisions is farther divided into great eras, 

 those of Paleozoic time being given in the annexed table. Each 

 era is in general divisible into three periods of time, the early, mid- 

 dle, and later, for which the prefixes palco (or co), nicso and nco are 

 used. The farther division of the periods is into epochs. 



During the continuance of each great time division of the geo- 

 logic history of the earthy more or less extensive rock systems were 

 deposited, wherever the conditions were favorable. Thus the Paleo- 

 zoic rock system is that deposited during Paleozoic time. That 

 part of the Paleozoic rock system which was deposited during the 

 Siluric era, is called the Siluric rock series, and similarly, the name 

 of each of the other great eras is also applied to the rock series 

 deposited during its continuance. In like manner each geologic 

 period has its corresponding group of rocks deposited during its con- 

 tinuance. These rock groups and their farther subdivision into 

 stages have, in New York, received local names, the name of the 

 locality where the rocks are best developed being selected. The 

 rocks formed during Proterozoic and Azoic time are generally 

 spoken of as pre-Cambric. 



The following table embodies the result of tile latest studies.^ 

 The thicknesses are chiefly obtained from well records published by 

 Prof. I. P. Bishop. The relations of these strata to each other in 

 this region are shown in the north and south section from Canada to 

 the New York-Pennsylvania line, presented in fig. i. 



Ever since the days of Lyell and Hall the life history of Niagara 

 and the origin of the Great lakes has engaged the attention of 

 geologists the world over. Among the names prominent in con- 

 nection with studies of the geology of Niagara in one or more of 

 its aspects, may be mentioned those of Bishop, Clarke, Claypole, 

 Davis, Fairchild, Gilbert, Hall, Hitchcock, Lesley, Lyell, Newberry, 

 Pohlman, Ringueberg, Shaler, Spencer, Tarr, Taylor, Upham and 

 Wright, besides a host of others. ^ 



^Clarke and Schuchert. Science, n. s. Dec. 15, 1899, 10 :3- It will be 

 found to differ in some respects from the table published in the author's 

 Geology of Eighteen Mile creek, etc. 



^In the field work I have had the efificient assistance of my friend Mr R. F. 

 Morgan of Buffalo. 



