216 



THE NATURALIST IN AUSTRALIA. 



ASCIDIAN-COYEKEl) ROCKS, ROEHVCK BAY, WESTERN AUSTRALIA 



W. Sai-ille-fenf, Photo. 



As matters stand, this rock may conveniently 

 serve as a guide-post to that particular spot in 

 the Bay, whence, when the tide was low, a con- 

 siderable number of the marine forms illustrated or 

 referred to in these pages were collected or ob- 

 served. 



Although so high up within the tropics, the 

 reefs of Roebuck Bay, which render navigation to 

 the port of Broome extremely intricate, are not of 

 coral, but are stratified replicas of the much-inter- 

 rupted friable red sand-stone cliffs that line the shore. 

 Coral grows here, but very sparingly compared with 

 a little farther to the north and east. In place of it, certain other marine organisms 

 are abundant to an extent that has not been observed by the writer on any other part 

 of the Australian coast-line. The zoological group most in evidence among the reefs 

 at low tide, at what is known as Entrance Point, close to the " Rhinoceros Rock " of 

 our Chapter heading, is that of the Ascidians. One particular type, referable to the 

 genus Colella, literally festoons every ledge and crevice of the much-eroded rocks in 

 such a manner that their aspect, as seen from a little distance, presents a remarkable 

 resemblance to stalactitic formations. The luxuriant growth of these Colellae, together 

 with the peculiar petrological resemblance suggested, will be recognised on a reference 

 to the accompanying corner illustration, which is composed of the joined-up replicas of 

 several photographs that were taken of contiguous areas. In the lowermost section the 

 Ascidians are taken from a nearer point of view, and being more considerably 



