ESTUARINE DEPOSITS l8l 



found. The excessive slowness with which this abysmal deposit is 

 formed, is shown by the occurrence, in recognizable quantities, of 

 meteoric iron, which reaches the earth in the form of meteorites, 

 or " shooting stars," and by the presence of the remains of animals 

 which have long been extinct. 



Of all the oceanic deposits the red clay is much the most widely 

 extended, covering 5 1,500,000 square miles of the bottom. Almost 

 four- fifths of this vast area are in the great depths of the Pacific ; the 

 shallower Atlantic has much more of the foraminiferal ooze than 

 of the red clay. The observed range in depth is from 2225 to 

 3950 fathoms. 



Comparing the marine deposits now accumulating in the sea 

 with the rocks of evidently marine origin which form most of the 

 land, we find that the great bulk of these rocks, the sandstones, 

 slates, and limestones, are such as are formed in water of shallow 

 and moderate depths, while only rarely do we discover a rock, like 

 chalk, that implies really deep water. 



VII. Estuarine Deposits 



An estuary is a wide opening at the mouth of a river into which 

 the sea has penetrated by the depression of the land. In such 

 bodies of water the tide often scours with much force. Estuaries 

 abound along our Atlantic coast, Delaware and Chesapeake bays 

 and the mouth of the Hudson being excellent examples of such. 

 The water in them is brackish, and unfavourable to abundant 

 aquatic life, for only a limited number of marine animals, and 

 fewer fresh- water ones, flourish in brackish w r ater. 



Estuarine deposits are, in general, much like those of the sea, 

 except that they are apt to be of a finer grain for a given depth of 

 water; muds are abundantly laid down, especially in the more 

 sheltered nooks and bays, with fine and coarse sands and gravels 

 in the more exposed situations. The sands are apt to show a 

 confused stratification from the conflicting currents and eddies in 

 which they are deposited, but with horizontal layers formed at slack 

 water. Extensive mud flats often surround an estuary, especially 



