HOUTMAN ABROLHOS ISLANDS. 145 



continental shelf and not against the coast. The water between the 

 Abrolhos and the mainland is only about 20-25 fathoms deep. Now it 

 is hardly likely that one would find on this shallow coastal strip of water 

 lying over the shelf a much colder zone nearer the bottom consisting of 

 water running in towards the land with a well marked layer of warmer 

 water running out on the surface. The temperatures, so far taken by me, 

 give no indication of such a state, the waters of the shelf appearing 

 homothermic. It must be remembered that there is frequently a considerable 

 sea running in this region, and with depths of only 20 fathoms it is likely 

 that homothermic water will result. 



The following figures are taken from those of the last Abrolhos 

 Expedition. Unfortunately they are few because we were usually close to 

 the islands working the lagoons or else to the leeside (the East). 

 Thursday, 28th October, between Wallaby and Easter Groups 

 towards open ocean. 



Surface ... 20' 6° C. 



15 fathoms ... 19-87° C. 

 Sunday, November 7th, between Easter Groups and Pelsarfc Group. 

 Surface ... 20-8° C. 



20 fathoms .... 20-3° C. 

 Friday, October 22nd, outside Easter Group. 



Surface ... 19-8° 0. 



Bottom ... 19-5° C. 



Many readings were taken in the lagoons, but they are useless from the 



above point of view — the surface and bottom temperatures were usually 



the same except that the extreme surface layer, on an absolutely calm day, 



was often higher as a result of the direct heating effects of the sun. 



If we examine the prevailing winds at the Abrolhos we shall see that there 

 is less evidence still in favour of a warm surface current blown out from the 

 coast accounting for the Abrolhos Fauna. 



Winds, Geraldton District and Abrolhos. 



Summer — From the middle of September to the middle of May, Southerly 

 winds are characteristic. 



Rest of Year — Winds variable, with occasional N.W. to W. gales of 

 moderate force and of usually short duration. 



Summer Winds — During the summer the Southerly wind blows almost 

 without a break and resembles the trade wind in character and in force. 

 In the early hours of the morning it is certainly in the form of a land 

 breeze, but is E.S.E. to S.E. and is light. About 9 a.m. it hauls to the S. 

 or S.S.W. and commences to freshen, blowing its strongest during the 

 afternoon and continuing very frequently until after midnight. It then 

 falls light and works back to the land breeze again. Very occasionally, 



11* 



