ELEMENTARY GEOLOGY, ETC. 21 



2,000 to 3,000 fathoms deep, extending between the Canary Islands and the 

 Azores ; while a broad belt of much higher level (nowhere deeper than 2,000 

 fathoms, and generally much less) and of a very irregular form, reaches to 

 about 55° west. Beyond this a very deep and almost unfathomable region, 

 everywhere more than 4,000 fathoms, and generally more than 5,000, extends 

 east and west between 35° and 40° north latitude, and 45° to 65° west longitude. 

 " The West India Islands are connected with the shallower bottom of 2,000 

 fathoms by soundings which nowhere exceed 3,000 fathoms, and in latitude 

 20° north and longitude 60° west the breadth of this shallower portion is sin- 

 gularly narrow. Further south there is a belt of very deep water (more than 

 3,000 fathoms) nearly parallel to the South American coast, and much nearer 

 the American than the African side. The steepness of the sea bottom is gene- 

 rally much greater near the American coast, the depression being nearly 20,000 

 feet in 500 miles almost everywhere on that side, except near the Gulf of Mexico 

 and the Caribbean Sea, in neither of which is there a depth of 1,000 fathoms in 

 any part." — Page 28. 



The account of the Geological action of the Tidal wave, given in chapter 



TV., is one of the least satisfactory parts of the Physical geology of the 



book ; and we cannot help doubting whether Professor Ansted himself 



could explain clearly his meaning in the following sentence : — 



M The tide wave is probably a very effective force with reference to the sea 

 bottom, and the transport of solid matter in deep water. Being a wave of the 

 first order, its velocity is far greater in deep water than in shallow ; and, if it 

 proceeded with uniformity and regularity, the velocity at a depth of one fathom 

 being eight miles per hour, at the depth of 10 fathoms it would travel as much 

 as 25 miles in the same time; at 50 fathoms, 57 miles ; at 100 fathoms, 80 miles, 

 at 1,000 fathoms, 250 miles ; and at 4,000 fathoms, 500 miles."— Page 58. 



Does Professor Ansted mean to assert that the Tidal wave travels with 

 such different velocities at different depths in the same sea ? If so, he has 

 studied the theory of tides and waves to but little purpose. Or, does he 

 imply, in this obscure passage, that the Tide wave is effective as a Geolo- 

 gical agent, in proportion to its velocity ? If so, we fear he has confounded 

 two totally distinct things — viz., the velocity of the Tide wave and the 

 velocity of the particles composing it. It is on the latter alone that the 

 Geological or Mechanical action of the tide, as a degrading and transporting 

 agent, depends ; and not at all on the velocity of the tidal wave, which 

 varies greatly, without any sensible alteration of the velocity of the indi- 

 vidual particles of the water. It is scarcely possible to conceive that our 

 author can mean that, in a sea of four miles deep, which is of common occur- 

 rence, there are tidal currents at the bottom sweeping along at the rate of 

 five hundred miles per hour ; and yet, it is difficult for a learner not to 

 suppose that this is implied in the above sentence. 



MINERALOGY. 



Professor Ansted, in bis preface, states that he has " carefully modified 

 the Mineralogy, retaining, however, in the main, the former method of 



