DEVONIAN AGE. 267 



(a. ) Interior-Continental basin. — The Hamilton beds consist of shales, separated into 

 two parts by a thin layer of Encrinal limestone, and in many places overlaid by a thin 

 limestone stratum called the Tully lime- 

 stone. In the annexed section, from the Fig. 524. 

 coast of Lake Erie (as given by Hall), the 

 Hamilton beds, 10 b, include (1) blue 

 shale, (2) Encrinal limestone, (3) Upper 

 or Moscow shale: the Tully limestone is 

 wanting. Above lie (10 c) the Genesee 

 slate, and (11) a part of the Portage group 

 of the next (Chemung) period. In the Section of Hamilton Beds, Lake Erie, 

 lower part of the Marcellus shale (the rock 



of the first epoch) in New York, there are also layers of concretions of impure limestone, 

 and these abound most in fossils; but the fossils of the shale are generally small. 



The flagging-stone of the Hamilton is quarried near Kingston, Saugerties, Cox- 

 sackie, and elsewhere on the Hudson, in Ulster, Gi'eene, and Albany counties, N. Y. 

 The bed is but a few feet thick. It breaks into very even slabs of great size. It is 

 almost without fossils, but is penetrated in many parts by the filling of a slender worm- 

 hole; and its surfaces are often marked with tracks of Mollusks. The Genesee slate 

 overlies the Tully limestone, when this is present. It is not recognized in the eastern 

 part of the State of New York. The limestone stratum of Illinois, referred to the Mar- 

 cellus and Hamilton epochs, is not over 120 feet in thickness. 



The Marcellus shale rarely exceeds in thickness 50 feet. The Hamilton strata are 

 1,000 feet thick in central New York, but not half this along Lake Erie. They are 

 also comparatively thin and more sandy on the east, in the Helderberg Mountains. 

 They are well exposed along the valleys of Seneca and Cayuga Lakes. The Genesee 

 shale is 150 feet thick near Seneca Lake : it thins westward, and is not over 25 feet on 

 Lake Erie. 



The Black shale is 350 feet in Ohio, and 10 to 60 feet in Illinois. In Tennessee, west 

 of the Cumberland table-laud, it has at top a thin layer of small concretions, and 

 below it, a bed of fetid limestone ; it outcrops on the slopes around the central basin 

 of the State. As no other rock intervenes between the Corniferous and Carboniferous, 

 this Black shale has been suspected to be Chemung, but without any satisfactory evi- 

 dence from fossils. A thin band of concretions at the top of this bed, in central Ken- 

 tucky, contains many remains of fishes, and also crustaceans, of the genera Colpocaris, 

 Soltnocaris, Archceocaris, the two former closely allied to Ceratiocaris. 



In Missouri, the Hamilton formation consists of about 50 feet of shale, with some 

 beds of limestone. In Iowa, there are 200 feet of shales and limestone, and no other 

 Devonian rocks. 



(b. ) Appalachian region. — In Pennsylvania, H. D. Rogers makes three divisions of 

 the Hamilton formation, a lower of black shales, which is 250 feet thick in Huntingdon, 

 a middle of variegated shales and flags, 600 feet thick at the same place, and an upper 

 black shale of 300 feet. In East Tennessee, the thickness is 100 feet. (Safford.) 



The thickness of the Hamilton formation east of central New York shows that this 

 region was at this time, as in the Oriskany period, on the northern border or limits of 

 the Southern Appalachian region. 



(c.) In the Eastern-border region, at Gaspe\ the 6,000 feet of sandstones, above the 

 1,100 referred to the Corniferous period, are believed to be for the most part of HamiL 

 ton age. St. John's, in New Brunswick, is a noted locality of fossil plants of this era. 



Ripple-marks. — The rocks of this formation, especially the Hamil- 

 ton beds, are remarkable for the abundance of ripple-marks on the 

 layers. The flagging-stone is often covered with ripple-marks and 

 wave-lines. The joints intersecting the strata are often of great ex- 

 tent and regularity. They have been referred to on page 88 ; and 



