Kinda looks like river washed conglomerate. From Google: Conglomerate
(pronunciation: /kəŋˈɡlɒmərᵻt/) is a coarse-grained clastic sedimentary
rock
that is composed of a substantial fraction of rounded to subangular gravel-size clasts, e.g., granules, pebbles, cobbles, and boulders, larger than 2 mm (0.079 in) in diameter.