Notices respecting New Booh. 49 



shoal will be forced over on tlie lee side. Accordingly we do find that 

 shoals shift, more particularly when near the surface", unless there be 

 an equal counteracting effect in a current or tide." 



Mr. De la Beche has collected scattered notices respecting the 

 various principal currents of the globe, and endeavours to show that 

 the hypothesis of their being sufficient to transport the detritus of the 

 land over the depths of the ocean, and from Europe to America, is 

 not founded on those facts which have been brought to light respect- 

 ing currents. He observes : 



"In estimating the transporting power of currents, we should con- 

 sider the causes which produce them, and the nature of the fluid in 

 which they are produced. The motion of the earth, although it would 

 seem to give a certain general movement to the waters of our globe, 

 would not appear capable, taken by itself, to produce currents of 

 geological importance. The great cause of ocean-currents would seem 

 to be prevalent winds j and accordingly we find that in the equatorial 

 regions of the world, over which the more or less easterly winds, 

 commonly called the trade winds, prevail, there is a tendency of the 

 waters to flow westward in the Pacific Ocean, in the Atlantic, and in 

 those parts of the Indian Seas free from the monsoons. That the 

 winds are the great cause of ocean-currents, is a fact sufficiently proved 

 by the velocity and direction of such currents in the Indian and 

 Chinese seas, varying with the force and direction of the monsoons. 



" The winds being, generally speaking, the cause of the great ocean- 

 currents, and effects being only in proportion to their causes, the 

 streams of water thus produced will not extend deeper than the pro- 

 pelling power of the winds can be felt. Now, as the ocean varies in 

 density according to its depth, the cause sufficient to move waters on 

 the surface, and to certain depths beneath it, will constantly meet 

 with opposition at an increasing ratio, until, finally, the moving power 

 and the resistance being equal, no effect whatever is produced ; and 

 all water beneath a certain depth would be, as far as respects surface 

 causes, immovable, and consequently would have no transporting 

 power. 



" Hence it would appear that the transporting power of currents 

 will depend on the depth of the sea, ail other things being equal ; and 

 that the smaller the depth the greater the transporting power. Conse- 

 quently, coasts are the situations wiiere we may look for this power." 



Throughout the work there are copious lists, derived from the best 

 authorities, of the various organic remains discovered in each group 

 of rocks, not only in the British Islands, but in Eurojje generally, and 

 even in some cases extending to India and North America. These 

 are for the most part accompanied by remarks relating to each col- 

 lection of such exuviae. While noticing the remains of vegetables and 

 animals which may be enveloped in the deposits formed during the 

 present order of things, Mr. De la Beche observes : 



"These will necessarily consist of existing animals, but may also 

 mclude some no longer found in a living state. Man not only greatly 

 modifies the present surface of the land by destroying tracts of forests, 



A^'-.S'. Vol. II. No. Gi. Jem. 1832. II ])rcventing 



