238 FOSBILIFEEOrS SILICEOUS DEPOSIT 



Chemical Analysis. 





Weathei'ed portion. 





Moisture, given off at 100° ... 



.. 4-16 



Combined water (loss on ignition) . 



.. r78 



Insoluble silica... 



.. 89-74 



Soluble silica ... 



•47 



Alumina and iron sesquioxide 



.. 1^13 



Lime ..; ...... 



•48 



Magnesia 



.. 1-98 



Loss ... ... ... ... 



•26 





10000 



Specific gravity, 2-046 at QQ° Fah. 

 Adheres strongly to tlie tongue. 



UmveatJiered portion. 



Water, given off at 100° 4-08 



Combined vrater (loss on ignition) ... ^48 



Insoluble silica... ... ... ... 91-67 



Soluble silica ... ... ... ... "30 



Alumina and iron sesquioxide ... 1"56 



Lime '36 



Magnesia ... ... ... ... '55 



Loss -90 



100-00 



Specific gravity, 2-S30 at 66° Fah. 



The composition shows that it answers to the common siliceous 

 einters or geyser deposits. 



It will be seen that the weathered specimen has a lower 

 specific gravity, and contains rather more water, also more lime 

 and magnesia. 



In places the structure is more or less distinctly lamellar, 

 evidently due to the manner of its deposition is successive layers. 

 The fracture is more or less distinctly conchoidal across the 

 planes of deposition, but where the lamellar structure is less 

 strongly marked or altogether obliterated, the fracture is con- 

 choidal in all directions. 



The weathered surface is usually marked with the remains of 

 ferns, which stand well out in relief ; with the ferns and stems 

 are the fruits and seeds of other forms of vegetable life. 



Within the substance of the mass occasional layers of a 

 brilliant white colour are met with, and along these layers it 

 splits into flakes and slabs with more or less ease ; these white 



