﻿118 GEOLOGICAL ACTION OF 



any commendation at my hands. He entered cordially into my views, assisted me 

 in gathering and arranging the details of this memoir, and supplied, from his abundant 

 stores of ready knowledge, the most conspicuous and valuable examples of tidal and 

 current action in past geological ages. 



It has been suggested by Mr. Desor, as well as by other friends in whose judgment 

 I have great confidence, and who, like himself, were not previously familiar with the sub- 

 ject of the tides generally or with the nature of tide-currents, that this memoir would 

 be more intelligible if it were preceded by a short treatise upon the dynamical action of 

 the tides, and of the streams generated by resistance to the motion of the tidal undula- 

 tions, or by other causes affecting the condition of the ocean. But it has been consid- 

 ered, on the other hand, that the object of this memoir is to introduce a new theory to 

 the notice of the scientific world, which has already in its possession the means of testing 

 the accuracy of the principles upon which the theory is based. The long and able 

 series of " Researches on the Tides," by Dr. Whewell, have supplied the necessary in- 

 formation on this subject; and any statements comprising such practical details as come 

 under the special observation of the hydrographer will be referred to competent authority.* 



The satisfactory treatment of this subject, moreover, would embrace a wide range, 

 commencing with the theoretical origin of the tidal currents, and terminating with graphi- 

 cal illustrations of the variable and complicated action of streams passing from the open 

 sea into wide bays, meeting in sounds, conflicting with the courses of rivers, or following 

 the irregularities of an indented and broken coast: it must also include some of the 

 ocean currents. It has been thought best, therefore, upon reflection, to defer a popular 

 account of the following views to another time and place. This account will embrace 

 the distribution of the coralline detritus, which belongs equally to the subject, though 

 designedly omitted in this memoir. 



Section I. — Upon Shoals, and their Relation to the Currents of that Part of the Sea in 



which they are found. 



There are certain inequalities in the bottom of the ocean, particularly that part of it 

 near the land, which give a distinctive character to the navigation of the region in which 

 they are found. The inequalities to which I refer are known by the generic name of 



* I have referred particularly to the "Researches" of Dr. Whewell, rather than the discussions of Sir 

 John Lubbock; because it is the form, progress, transmission, interference, &c, of tide-waves, and the 

 establishment of ports, that are to be dealt with, and not those variable phenomena of the tides depending 

 upon changes in the moon's place or upon atmospheric influences. 



