UPON ROCKS OF THE NEW YORK SYSTEM. 427 



At some future time I hope to be able to offer to the Associa- 

 tion the resuhs of more extended observations. In the mean time, 

 the object has been to call attention to the facts, in the hope that 

 the observations of others would be dkected to the same subject, 

 and by this means new light would be thrown upon the matter, 

 or some more satisfactory explanation given of the cause of the 

 phenomena. 



Wave Lines. 



There are still another kind of markings, which are presented 

 as minute ridges upon the surface of sfrata, scarcely raised above 

 the uniform level, yet perfectly defined, pursuing no definite di- 

 rection, but always more or less curved or undulating. These 

 are not as common as the forms just described, and appear only 

 for limited distances. The most decided and best characterized 

 which I have seen, are in the Medina sandstone, and confined to 

 strata forming but a small portion of this rock, appearing neither 

 above nor below this position. 



Plate XVII, fig. 4, copied from the Report of the Fourth Ge- 

 ological District of New York, will give an illustration. The sur- 

 face, from which this is reduced, is about five feet long by three 

 wide, being a slab quarried about one mile north of Lockport. 

 The figure illustrates perfectly the manner in which these lines 

 occur. From the inner side of each cm-ve there is a slight elevation 

 in passing outward, but which slopes gradually down to the surface 

 beyond. I have called these markings umve lines, from their 

 perfect similarity to the lines or ridges left upon sandy beaches by 

 the retiring wave. 



Any one, who has passed some time upon the bays of the 

 ocean, bordered by almost level sandy beaches of many rods in 

 width, will not fail to have noticed, that each retiring wave leaves 

 behind it a small line or ridge of sand. It frequently happens, 

 that from the ebbing tide or the lulling of the wind, each suc- 

 cessive wave reaches less and less high up the beach ; and 

 consequently a succession of these lines is left, till the rising 

 tide or wind brings back the water and obliterates them. 



The same appearances are beautifully exhibited upon the 



