66 



DEPTHS OF THE OCEAN 



distinct assemblage of animal and plant life in the upper 

 water-layers. 



On the morning of 

 Monday 25th April 

 we anchored off Gib- 

 raltar, where we had 

 our boilers overhauled, 

 and procured reserve 

 rollers and blocks, as 

 well as new swivels 

 for the trawl line. 



Currents in During our stay at 



GibfSil''^ Gibraltar we made two 



short trips : one to 



the Strait to study the 



currents, and the other 



to the Mediterranean 



to test our pelagic 



appliances. The 



Strait of Gibraltar has 



for a long time past attracted the attention of hydrographers. 



Through this narrow channel the exchange of water between 



Fig. 45.— roRTUGUESE Fisherman. 



Fig. 46. — Pelagic Crab [Polyhius henslowi, Leach). Nat. size. 



the Atlantic and the Mediterranean takes place, and there are 

 great fluctuations in the two streams. A knowledge of the 

 laws that govern the currents of this marine thoroughfare 



