. Bulletin of the Department of Geology. Geology. 1914] Lawson: Ore Deposition by Meteoric Waters 225 equally well affect the igneous rock itself; although it is probable that the fracturing is inaugurated beyond it by collapse due to crystal- lization. Certain veins in volcanic rocks in Nevada, which came under my observation a few years ago, I ascribed in an unpublished report to shrinkage by cooling of an intrusive mass. The temperature of the region in which shrinkage cracks should begin to form would be but little less than the melting-point of the magma, and therefore well above the lowe
. Bulletin of the Department of Geology. Geology. 1914] Lawson: Ore Deposition by Meteoric Waters 225 equally well affect the igneous rock itself; although it is probable that the fracturing is inaugurated beyond it by collapse due to crystal- lization. Certain veins in volcanic rocks in Nevada, which came under my observation a few years ago, I ascribed in an unpublished report to shrinkage by cooling of an intrusive mass. The temperature of the region in which shrinkage cracks should begin to form would be but little less than the melting-point of the magma, and therefore well above the lower limit of the range specified by Lindgren. The neces- sary conduits and temperature being thus provided, we may proceed with the question of circulation. Referring to the diagram, figure 1, which is a graphic epitome of our assumed conditions, it is apparent A. Fig. 1. Ideal sketch of an intrusive mass of the Monzoni type in stratified rocks which dip toward the intrusion, to explain the possibility of the circula- tion of heated meteoric waters on the periphery and through it. that water entering at A and B and following the stratification will tend to keep the lower part of the syncline saturated. The intrusive mass provides conduits transverse to the stratification at C-C, initially by disruption and subsequently by shrinkage, and it also creates a high temperature in the rupture zone. If the temperature were uniform throughout the region included in the diagram, the movement of the water would be up at C on the artesian principle. If the temperature at C be high and that at A be low, the artesian principle operates a fortiori, a short column of superheated steam being lighter than a long column of water. As the steam is drawn off above C the supply is replenished from A and B, so that a prolonged circulation is main-. Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of the
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