CHARACTERISTICS OF CORROSION CONGLOMERATE 273 



weeds rather than to the usual force of waves is frankly admitted here to 

 be because it appears impossible for waves to have made such pebbles. 

 The amount of waste or wear of the pebbles was great. It has reduced 

 them to a half or a tenth of the bulk of the original limestone pieces, 

 yet it has not reduced them to uniform size or shape. The pebbles have, 

 of course, a flattened and smoothed appearance, but the raised or jutting 

 parts of them are not more worn than are hollows and depressions of the 

 surfaces. Their edges are not regularly rounded, as is the case with 

 well-worn beach pebbles, but rather their edges are sharp and thin and 

 often jagged. 



Chaeacteeistics of Coeeosion Conglomeeate 



general characteristics 



The characteristics of marine corrosion conglomerate — the features by 

 which such deposit is to be recognized — can perhaps not be fully deter- 

 mined from its occurrence in one place. The features of the conglom- 

 erate here described are, briefly, the follomng: The pebbles are lime- 

 stone in either shaJe or shaly limestone as matrix. They have a black 

 and more or less smoothed surface. Their surface is rounded convex and 

 concave or pitted and jagged. They are often flat and sharp edged, but 

 retain more or less of the original shape of the limestone lenses and 

 nodules from which they derived. The fossil contents in the pebbles are 

 the same as those that characterize' the strata in which they lie. 



COMPOSITION OF PEBBLES 



In case of other conglomerates which like this one formed at some dis- 

 tance from the shore, some, if not all, of the same features should be 

 found on them and may be recognized. Such a conglomerate, for ex- 

 ample, should contain limestone. A relatively soluble rock, such as a 

 limestone, is the only one which when broken on the sea-floor would be 

 corroded readily so as to form conglomerate. A sandstone with lime 

 cementing material might, of course, be made into pebbles, and the in- 

 soluble concretions, chert, etcetera, from a disrupted limestone might 

 also mingle with pebbles of limestone; but those materials other than 

 limestone might seldom, if ever, be perceptibly corroded or blackened. 



COLOR 



The black stain, together with smoothed corroded surface, is a marked 

 characteristic in the conglomerate here described, but in other cases the 

 black stain might be inconspicuous — for example, where the matrix is 



