274 ANALYSES OF SOILS. 



therefore do not exist originally in the organic matter, but are a result brought about by 

 the processes to which they have been subjected. 



Tlie rocks under consideration are usually concealed by a great amount of their own 

 debris. It is therefore impossible to determine their thickness or their extent ; they are, 

 however, between one lumdred and fifty and two hundred feet tliick. 



We have already stated that the shales contain beds of gypsum. The lowest beds are 

 merely thin inconsiderable masses, unfit or unprofitable for working ; yet the amount of 

 plaster is considerable. The rock itself, with its plaster, would form a very valuable 

 manure in many parts of the State. The decomposing shales, when plaster is wanting, 

 may be regarded as valuable as gypsum, and perhaps jnore so ; they have not, however, 

 been employed, and hence have not received the sanction of experiment or trial. 



In addition to the plaster beds, the shales embrace a singular deposit, which was called 

 by Mr. Eaton vermicular Umerock. This deposit, however, is not entitled to a distinct 

 name, inasmuch as it is subordinate to the shales, and forms but an inconsiderable mass 

 in the group. The vermicular rock is an impure limestone, and is composed of the fol 

 lowing elements : 



Water 0-23 



Organic matter 2'54 



Silex 3-30 



Carbonic acid ..20-62 _ 



Alumina 5'33 



Magnesia 4-20 



Carbonate of lime 13*76 



Protoxide of iron a trace. 



50-04 in 50 parts. 



The main deposit of plaster is above those porous strata, the composition of which 

 has been furnished in the preceding pages. 



The soft green shales pass into thin-bedded limestones, quite compact and hard, and 

 which, on being struck, emit a sharp ringing sound similar to clinkstone. These thin beds 

 contain the hydraulic limestones, which have been described. 



These parts of the series differ considerably in composition from those below. According 

 to Dr. Beck, their composition (the water-limos) is as follows : 



Carbonic acid 39-80 



Lime 25-24 



Magnesia 18-80 



Silica and alumina 13-50 



Peroxide of iron 1-25 



Moisture and loss . 1-41 



100-00 



