72 Xorth American 



niiig'iiesian limestone, locally Jirenuceoiis ; (b) a light gray or 

 nearly white limestone, with some brown Liyers interstratified, 

 and when free from chert, composed of nearly pure calcium 

 carbonate. Chert and hornstone are abundant in both beds in 

 seams and nodules. 



The Burlington series appears jis far west ns Lake Valley, New 

 Mexico, also in the States of Iowa, Illinois and Missouri, On 

 the eastern and southern borders of the Illinois coal fields, no 

 calcareous beds have yet been found occupying the horizon to 

 which this series proi)e]'ly belongs. The Burlington grou]), as 

 far as known, only contains Pliillipsia tuber cidata. Meek and 

 Worthen. 



Keokuk Series, — This rock, in its full development, consists 

 of a gray or bluish-gi-ay compact, encrinal limestone, in beds 

 sepjirated by shaly partings ; while bands of shale oi- mail of 

 considerable thickness sometimes occur. At the base of the 

 limestone a series of chei'ty beds ai">])ears, which resist denuda- 

 tion, and now form the i-iver-bed above Keokuk, Iowa, producing 

 ra})ids. At this |)()int they have a total thickness of 00 feet, but 

 fuither to the scnith they become greatly augmented and produce 

 the body of stra'a known as the Silicioits series in Tennessee. 



The foUowing Irilobites a[)peai' in this series : Griffithides 

 PortlocM, Griffithides bufo. 



St, Louis Series. — At St. Louis and Alton, these beds con- 

 sist of regulai'ly bedded gray, or bluish gi-ay limestone, sometimes 

 massive, and ao-ain in thin beds, su i table for flao-(rino--stones. Near 

 the middle of the series, between Alton and the mouth of the 

 Piasa, a bed of concretionary and brecciated limestone of about 

 20 feet thick appears ; below this, the limestones are of a darker 

 color. North of the Illiiiois I\iver, the series thins out rapidly. 

 In the southern portions of Illinois, the beds change their litho- 

 logical character to a light oolitic limestone, with a thin-bedded 

 cherty limestone at its base. In Indiana, the St. Louis series 

 includes the Spergen HillWrnQ^iowe, ar.d also an excellent build- 

 ing stone at Ellettsville. In Kentucky, rocks of this series ap- 

 pear on the railroad between Elizabethtown and Paducah ; the 

 top beds consist of an oolitic limestone, alternating with beds o^- 



