170 Notices of Memoirs—Prof. Edward Hull— 
such chlorine occurs, sometimes in considerable quantity, in com- 
bination with sodium, magnesium, and potassium. Spring water 
coming as it does directly from the strata, or from rocks of various 
kinds, is generally free from any external or artificial ingredients, 
hence it may be regarded as the chief source of supply of the 
carbonates and salts found in streams and rivers. If we enquire 
what is the origin of spring water, the reply is simple. It is 
water which originally falling on the surface as rain or snow has 
percolated downwards into the rocky crust, and taking up the 
soluble matters with which it comes in contact, bursts forth at the 
surface along lines of fault, fissure, or other natural ducts. The 
relative proportions of the ingredients of sea water and of rivers or 
lakes may be gathered from the selected examples on p. 171. 
16. From the above results of the analysis of various waters, it 
will be seen that there is no essential difference between the waters 
of the ocean and those of lakes and rivers except in the proportions - 
of the dissolved ingredients. There are, of course, occasionally 
substances specially abundant, as is the case with bromine in the 
waters of the Dead Sea, probably derived from the volcanic district 
on its borders; on the other hand, silica (Si O?), which is not 
mentioned in the waters of the Atlantic Ocean in the analysis of 
Von Bibra, is certainly present in those waters, and supplies 
the material from which sponges, diatoms, and radiolaria build up 
their skeletons. It will be observed also that chlorine and sulphuric 
acid is present in all the waters, and these gases uniting with the 
alkalies, give rise to the salts which are so abundant in the waters 
of the ocean and of closed lakes. 
17. In considering the manner in which springs and surface 
waters have become impregnated with salts and carbonates, we have 
to recollect that all rocks decompose in presence of the atmosphere. 
This is mainly due to the carbonic acid (carbon-dioxide) contained 
in the air and rain water, which acts upon felspathic rocks, com- 
posed, as we have seen, of double silicates of alumina, potash, and 
soda. KHbelman has well explained the process by which basaltic 
and similar rocks are decomposed under the influence of the 
atmosphere. The carbonic acid (carbon-dioxide) combines with the 
lime and magnesia, while the silica is liberated in a soluble form. 
The felspar is more stable than the pyroxene and hornblende, but it 
ultimately gives way, forming a hydrous silicate of alumina. Thus we 
can account for the presence of carbonates of lime and magnesia, 
free silica, and by a further process in presence of sulphuric acid and 
chlorine of the various sulphates and chlorides. 
18. Now, as bearing on the fact of sodium chloride (or common 
salt) being the chief ingredient in oceanic waters, as well as in those 
of the Dead Sea and most salt lakes, we must recollect that the 
soda-felspars are much more soluble than the potash-felspars, and 
on this account we have probably a true cause of the predominance 
of sodium chloride. The rocks composed in the main of such 
felspars as labradorite, albite, oligoclase, and andesine, were there- 
fore more powerfully acted upon than those composed of orthoclase 
