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Cincinnati Society of Natural History. 



FOSSIL MUD-MARKINGS. 



If such are the effects of rain on modern mud banks, the inference is 

 just that if similar markings are found in the rocks, they were produced 

 by similar causes. Like causes produce like effects ; so that, as specimens 

 of rock have been found containing impressions like these rain-drops, it 

 may be considered that they were made in the same way. Dr. Dawson, in 

 ''Acadian Geology," p. 27, figures rocks from the Carboniferous with rain- 

 drop impressions. Lyell, in "Travels in America'' (first visit), Vol. II., 

 p. 140, refers to similar ones from the red sandstone of New Jersey; and 

 quite recently Mr. U. P. James has found in Clinton County, Ohio, in strata 

 ot the Cincinnati group, exactly similar markings, as shown in Plate V., 

 figure 2. 



The inferences from these facts are evident. The marks could have been 

 made in no other way than on mud beaches alternately bared and covered 

 by the tide. And if this is the case, it becomes proof positive that part 

 of the strata, at least, was deposited in shallow water or on the margin of 

 the ocean. It has been thought that the strata of this group were depos- 

 ited in deep water, but facts are known now which are sufficient to prove 

 the reverse. Some of these will be given presently. 



CLASSIFICATION OF THE FUCOIDS. 



The fossils which have been referred to fucoids may be classified under 

 three different heads: 1. Mud marks, concretions or rain marks; 2. Tracks 

 or trails of annelids, mollusks or crustaceans: 3. Probable Alga?. Of 

 these, the last are the least and the second are the most numerous Taking 

 them in order, mud marks, and so on, come first under consideration. 



FUCOIDAL MUD MARKS. 



Next to the rain-drops on mud flats- or banks come mud bubbles. These 

 are often seen— sometimes perfectly circular, one-half to three-quarters ol 

 an inch in diameter, and are of liquid mud, strong enough to stand consid- 

 erable "pressure without bursting. (Plate V.. figure 3.) These are repre- 

 sented in the rocks of the Cincinnati group by a form which has been de- 

 scribed as a fucoid under the name of Discopliycus typicalis. Walcott. 

 "Trans. Alb. Inst.," Vol. X.. p. 19; (Plate V. , figure 4.) This is described 

 as being almost circular, flat, and with a corrugated or furrowed edge, as 

 it' a rather succulent material had been wrinkled under pressure. In the 

 strata of the Utica slate, sometimes considered as Cincinnati group, another 

 form was described by Walcott (in "Trans. Alb. Inst.," Vol. X., p. 19) as 

 Cyathophycus subsphericus. (Plate T. , figure 5.) The apex of this has 



