Structure of some Silicious Sponges. 351 



the Cliona, Alcyonium, Lobularia, &c. It is interesting to ob- 

 serve, that the earthy matter of the skeleton of these earhest in- 

 habitants of the ocean, is the same with what we know to have 

 paved the bottom of the vast abyss at the remotest periods we can 

 reach of the earth's history, whether we imagine the silica of the 

 primitive rocks formed by the oxidation of the solid surface, or 

 precipitated from the superincumbent fluid. The appearance of 

 many of their crystalHne silicious pointed spicula is the same 

 with that of the slender hexaedral acuminated prisms which si- 

 lica naturally assumes in the crystallized state ; and the silicious 

 crystals formed by nature contain cavities and fluids like those 

 formed by organic life. The laws, therefore, which regulate 

 the forms of the simplest sihcious spicula composing the skeleton 

 of the marine sponge, do not appear to difler much from those 

 which regulate the forms of brute matter. 



Notice of a Voyage of Research. In a Letter from Captain 

 Basil Hall, R. N., to Professor Jamesox. 



X N answer to your questions as to what would be the most 

 useful objects of inquiry, were a voyage undertaken for the ex- 

 press purpose of research, I beg leave to offer you the following 

 remarks, — the result of a good deal of reflection on the subject, 

 and of some personal experience of those points in the investiga- 

 tion most important in practice. 



Voyages of discovery, as they were formerly called, seem now 

 at an end ; since all, or very nearly all, the navigable parts of 

 the earth have been pretty well explored. Much, however, re- 

 mains to be done, in order to complete the work commenced 

 by former voyagers, in a manner suitable to the greatly improv- 

 ed means, and the still more enlightened ideas, of the day. 



It may assist your apprehension of the subject, to class the 

 different objects of inquiry under distinct heads, that their im- 

 portance may be examined separately. 



First, To make observations having direct and immediate 



