Conglomerate

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Rock class: Clastic Sedimentary Rock
Color: Varies considerably
Grain: Pebble diameters larger than 4 mm (0.16 in); matrix grains larger than 2 mm (0.08 in)
Environment: Conglomerates form when gravel consolidates in shallow and turbulent water, such as occur with torrential fluvial deposits or marine transgressions.
Uses: Building stone.
Comments: Conglomerates are among the most fascinating of rocks because every conglomerate poses a mystery, the solution of which will be a complex story. Consider the inferences drawn in one example as described by John McPhee, {\i Annals of the Former World,} p. 217: ÒIt has been AnitaÕs style as a geologist to begin with an outcrop and address herself to history from there--to begin with what she can touch, and then to reason her way back through time as far as she can go. A river conglomerate, as tangible rock, unarguably presents the river. The river speaks of higher ground. The volume of sediment that the river has carried can imply a range of mountains. To find Precambrian jaspers in the beds of younger rivers means that the Precambrian, the so-called basement rock, was lifted to form the mountains. These are sensible inferences....Ó Related Terms Clasts = the pebbles included in the conglomerate. Matrix = the cement that holds the clasts together. Monogenetic conglomerate = when the clast pebbles are of a single type. Polygenetic conglomerate = when multiple types of rock are present. Puddingstone = conglomerate containing rounded flint clasts. If the clasts are mostly angular instead of rounded, then the rock is breccia instead of conglomerate (see breccia page). Recommended reading John McPhee, {\i The Control of Nature,} Part 3, ÒLos Angeles Against the Mountains.Ó (Cf. the mass movement section of an introductory geology textbook such as Stanley Chernicoff, {\i Essentials of Geology.}) [conglomerate.jpg]

Rock class:	Clastic Sedimentary Rock
Color:	Varies considerably
Grain:	Pebble diameters larger than 4 mm (0.16 in); matrix grains larger than 2 mm (0.08 in)
Environment:	Conglomerates form when gravel consolidates in shallow and turbulent water, such as occur with torrential fluvial deposits or marine transgressions.
Uses:	Building stone.
Comments:	Conglomerates are among the most fascinating of rocks because every conglomerate poses a mystery, the solution of which will be a complex story. Consider the inferences drawn in one example as described by John McPhee, {\i Annals of the Former World,} p. 217: ÒIt has been AnitaÕs style as a geologist to begin with an outcrop and address herself to history from there--to begin with what she can touch, and then to reason her way back through time as far as she can go. A river conglomerate, as tangible rock, unarguably presents the river. The river speaks of higher ground. The volume of sediment that the river has carried can imply a range of mountains. To find Precambrian jaspers in the beds of younger rivers means that the Precambrian, the so-called basement rock, was lifted to form the mountains. These are sensible inferences....Ó Related Terms Clasts = the pebbles included in the conglomerate. Matrix = the cement that holds the clasts together. Monogenetic conglomerate = when the clast pebbles are of a single type. Polygenetic conglomerate = when multiple types of rock are present. Puddingstone = conglomerate containing rounded flint clasts. If the clasts are mostly angular instead of rounded, then the rock is breccia instead of conglomerate (see breccia page). Recommended reading John McPhee, {\i The Control of Nature,} Part 3, ÒLos Angeles Against the Mountains.Ó (Cf. the mass movement section of an introductory geology textbook such as Stanley Chernicoff, {\i Essentials of Geology.})