312 Specific Gravity of Rocks. 



Messrs. Conybeare and Sedgewick, in the continuation of that 

 admirable work, The Geology of England and Wales, of which 

 the first volume has already given so much distinction to the 

 name of Mr. Conybeare. Since the history of the primary rocks 

 can receive no assistance from organic remains, we have nothing 

 left to determine with accuracy the character of those rocks but 

 their constituent minerals. And as the English language on this 

 continent and in Europe, is destined to be spoken by the most 

 important family of civilized society, we trust those gentlemen 

 will give appropriate scientific names cognate to the English 

 tongue. We despair of a universal nomenclature, and the sooner 

 we have a well considered one, accommodated to our own ovei'- 

 spreading language, the better. 



We now proceed to give the table of specific gravities of the 

 rocks used in constructing the Delaware Breakwater, for which, 

 together with the preliminary information, we are indebted to 

 that intelligent officer, Major Bender, of the United States 

 Army. — Editor. 



SPECIFIC GRAVITIES OF THE ROCKS USED IN THE CONSTRUC- 

 TION OF THE DELAWARE BREAKWATER. 



Communicated by Major George Bender, United States Army. 



" The two straight insulated stone dikes which form the work, 

 are constructing on a clayey anchorage ground, in a depth of 

 water from twenty-seven to thirty-four feet below the lowest 

 spring tides. The principal one is to be twelve hundred yards in 

 length, measuring from a point five hundred yards distant from 

 the line of twenty-four foot water, near the extreme point of 

 Cape Henlopen, and running in a W. N. W. direction from said 

 point. At the distance of three hundred and fifty yards from the 

 westernmost end of this, the other has also been commenced, and 

 is to run W. by S. five hundred yards. These dikes, or islets of 

 stone, are both to have a height of five and one third feet above 

 the highest springtides, with a breadth at bottom of one hundred 

 and sixty-seven feet, and at top twenty-two feet. The inner 

 slope is made to assume an angle of forty-five degrees, while the 

 outer has one hundred and six feet base to thirty-nine altitude, 

 and being covered with blocks of stone weighing from three to 

 five tons, and upwards, from six feet below low water, to the 

 summit, is such as experience has shown that the sea will break 



