why are cobbles and boulders composed of
Tillite is a lithified till (poorly sorted glacial debris) which may be called a matrix-supported conglomerate if there are enough granules, pebbles, cobbles, and boulders present. At least 30% of the rock should be composed of clasts larger than 2 mm in diameter in order to call that rock a true conglomerate.Conglomerate from the Ordovician near Bergen in Norway. The clasts are made of quartzite and are slightly flattened due to metamorphism.onglomerate is composed of clasts larger than 2 mm which is the upper limit of sand grains size. Conglomerates are differentiated from sedimentary breccias which are composed of angular clasts.