ever, occurring in sandstones and limestones of Tertiary age, doubtless were formed in place, and owe their deposition to the circulation of siliceous waters through the rocks. The distribution of gems through a rock or gravel matrix is not usually uniform. The gems more commonly occur in pockets, so called, the location of which seems to be governed by no law as yet dis­covered. Where crystallization of minerals has taken place about a fissure or open cavity, the minerals are more likely to be clear and free from inclusions than where formed in the mass of the rock itself.
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