184 Bibliography. *. 
Dr. Jackson has furnished a lucid account of the minerals that are * 
essential to the constitution of rocks. He remarks that silex, the 
most abundant substance in the globe, enters into the composition of 
all plants, and Prof. Liebig, in his recent work on the Chemistry of 
Agriculture, has shown that the silex is always taken up by plants in 
the form of silicate of potash; for, the decomposition of the primary 
rocks to form the basis of our soils, furnishes both materials in abun- 
dance. Silex is also, in vast quantities, the petrifying material of my- 
riads of animalcules* beneath peat bogs and in marshes and swamps. 
The fixed alkalies, potash and soda, found in the proportion of 10 
to 17 per cent. in the feldspar of granite, have not yet been extrica- 
ted from the feldspar by any process for the use of the arts, but they 
are constantly evolved by the natural decomposition of the mineral, 
probably in a great measure by the action of the carbonic acid of the 
atmosphere and by the vegetable acids. 
The granular quartz or firestone of Woonsocket, a member of the 
“mica slate formation, is used by all furnaces in the Atlantic States. 
The mica fuses, and thus agglutinates the grains more firmly together. 
Dr. Jackson is decidedly of opinion that the hornblende rock is of 
igneous origin ; it sometimes passes into serpentine, and is associated 
with soapstone and magnesian carbonate of lime, (dolomite,) whose 
origin it is supposed may be from the transfer of magnesia from the 
hornblende rock to the limestone, “by some unknown chemical ‘.. 
cess,” in accordance with the theory of Von Buch. Is not this a ease 
where the proposed explanation presents a greater difficulty than the 
one it proposes to solve?‘ Hornblende rocks yield by their decom- 
position an admirable soil, warm and of good texture.” 
The magnesian limes of Rhode Island are much esteemed “ for the 
quickness of their setting when converted into mortar, as also for the 
beautiful whiteness of the lime.” Hence the lime made from the Smith- 
field “ hard jointer” rock, commands a higher price than any other. 
In Rhode Island, the transition slates, instead of being filled, as 1 
usual elsewhere, ‘ with fossil trilobites and marine shells, contain an 
immense number and variety of eryptogamous and cellular plants,” 
the usual attendants of coal strata; “and in this deposit occur all the 
beds of anthracite of Rhode Island and Massachusetts.” 
“At the junction of the slates and granite rocks, various remarka- 
ble metamorphoses are seen, and the clay slate is either cemented into 
mica slate, flinty slate, or even scorie filled with epidote, as May “ 
seen on Newport Neck.” 
Dr. Jackson is of the opinion that both on the eastern and wester™ 
continents, a great deluge of waters has rushed from the north south- 
Se 
+ * Or Conferve, see notice in this No. p. 174. 
