80 



Before the close of the age, the ^vater had become pure 

 enough for the growth of crinoids, the remains of which, 

 together with the fronds of the branching bryozoan Sticto- 

 pora incisurata, and the shells of the small brachiopod 

 Xucleospira concinna, make up the greater portion of the 

 "Stictopora" bed. The age closed with the deposition of a 

 few inches of mud, in which few remains were buried. 



The conditions, however, were now favorable for the 

 re-establishment of a coral reef, which began by the growth 

 of large heads of Favosites hamiltonise. Cup corals soon 

 made their appearance again, though they were of different 

 species from those found in the Corniferous reef. This w^as 

 to be expected, for the many vicissitudes which the old 

 Corniferous corals passed through, would undoubtedh- 

 effect specific if not generic modification. Crinoids, too, 

 reappeared, though the genera and species were widely 

 difiterent from those which grew on the Lower Devonian 

 coral reef. The Encrinal limestone is this much modified 

 coral reef, which by its slight thickness indicates a compara- 

 tively short period of duration. 



This reef was also of less areal extent than its predecessor 

 in early Devonian times. The Encrinal limestone is not 

 recognized in the eastern portion of the State of New York, 

 and it has not been traced westward. In Illinois, Iowa, 

 Alichigan, Ohio, Indiana and other central states, however, 

 the Hamilton is chiefly represented by limestones, often 

 of considerable thickness, and in these, corals of various 

 kinds abound, thus showing that the Encrinal limestone 

 represents only a temporarv eastward extension of the coral 

 reefs which were forming in the clearer Avaters of the Central 

 Interior Sea. 



With the close of the short Encrinal limCvStone age, the 

 corals did not become suddenly overwhelmed as was the 

 case with the Corniferous reef. In fact, we find that after an 

 interval, a number of corals appeared which did not grow 



