1818.] ON THE FORMATION OF ROCKS. 261 



The instrument, and its necessary appendages, are ar- 

 ranged in a small box, so as to be very convenient, and 

 very portable. 



Your committee after a due consideration, and an ac- 

 tual trial of this apparatus^ are of opinion, that, for facility 

 and rapidity of operation, it has the advantage over every 

 other that has hitherto been proposed for the same pur- 

 pose; and they therefore cheerfully recommend it to the 

 attention of the Academv. 



They propose that it should be named Liikens^s Hy- 

 drostatic Balance, 



All which is respectfully submitted. 



IFilliam Maclure, 

 i?. M, Patterson, 

 Isaac Lea, 



Essay on the Formation of Rocks, or an Inquiry into 

 the probable Origin of their present Form and Struc- 

 ture. By William Maclure. 



Our knowledge of%e actual and present state of the 

 substances which constitute our globe, is unfortunately 

 confined to a small portion of the surface; from which it 

 would appear, that we are still ^-ery deficient even as to 

 those facts which are within the reach of our observation 

 and experience, and which may perhaps be necessary to 

 the forming of any rational conjecture, concerning the for- 

 mation or former state of those substances which cover 

 the external surface of the globe. 



Concerning the nature and properties of the great 

 mass which constitutes the interior of the earth, we are 



