Devonian Shales of Northern Ohio. 193 



region, to which on account of the plant-like Zoophites abounding- 

 in it the name corralline zone has been applied."* 



If the sea-bottom fauna thus described by Forbes were ele- 

 vated and the entombed remains of the Laminarian and coral- 

 line zones of the Irish sea should be studied by paleontologists, 

 some of them would doubtless assert, as they do of the Cleve- 

 land and Huron shales, that " it is certain that we are dealing 

 with overlapping formations" in the deposits of the coralline 

 zone. In a general way the fauna of the Chagrin shale in 

 northeastern Ohio bears a relation to that of the Cleveland and 

 Huron shales very similar to that which the Laminarian and 

 coralline zones sustain to each other in the British seas. Cor- 

 responding to the Laminarian zone, rich in seaweeds and shell 

 iish, there is in the Chagrin of northeastern Ohio a very 

 populous molluscan fauna associated with the impressions of 

 great numbers of seaweeds. Farther west, where these have 

 disappeared, we find the great predatory fishes of the Cleveland 

 and Huron shales which appear to have represented the domi- 

 nant forms of life in the deeper parts of the Ohio Devonian 

 sea just as large fishes are said to do in the present British seas. 



The foregoing discussion indicates the analogous character 

 of the differences existing between the faunas found in differ- 

 ent areas of the Ohio group and those which distinguish two 

 of the faunal zones of our present seas. The futility of 

 attempting to use such differences as evidence of distinct and 

 overlapping sea deposits becomes quite evident after these facts 

 have been pointed out. 



There remains still to be considered the rather marked litho- 

 logic differences which distinguish the Chagrin from the 

 Cleveland and Huron shales. Could the fine-textured black 

 carbonaceous shale found between Cleveland and Sandusky 

 have been deposited in the same sea at the same time as the 

 light colored sandy Chagrin shale of northern Ohio ? If 

 Ulrich's doctrine of the " persistence of lithologic units" is 

 true, they can not be synchronous deposits and they must be 

 successive or overlapping formations. Let us examine this 

 doctrine in the Hght of some of the observations which have 

 been made on the processes of sedimentation now in operation. 

 Tyndall'sf observations on the varying amounts of suspended 

 matter in the sea water at different points off the southwestern 

 coast of Europe are pertinent to this question. He found the 

 amounts of suspended matter in the sea water to differ widel}* 

 at different points. Sometimes the change was abrupt, as at a 

 point 14 miles off Cadiz harbor : " Here there is a sudden 



* Forbes, Edward : On researches into the natural history of the British 

 seas ; Edinburgh New Phil. Jour., vol. 1, pp. 335-339, 1851. 

 t Tyndall, John : Fragments of Science, pp. 127, 128. 



