John Smith Flett

“ On account of the imperfect stratification it is often very hard to estimate the thickness of conglomerates, and this difficulty is increased by the fact that many of them must have been laid down as sloping banks of pebbles and not as flat layers of deposit. Conglomerates are merely consolidated gravels, and have originated mostly on seashores or in shallow waters near land. They are typical shore formations, and are especially frequent where one series of stratified rocks rest upon an older group unconformable. ”

“ Igneous rocks on account of their toughness are also very abundant in many conglomerates; those at the base of the Old Red Sandstone of Scotland, which are thousands of feet in thickness, consist largely of andesite, porphyrite, granite, diorite and porphyry, along with vein-quartz, quartzite and various kinds of gneiss. Soft and friable rocks, on the other hand, such as shale, mica-schist and coal, are rarely found in any quantity as pebbles in conglomerate-beds. They are ground to pieces by friction against harder masses and help to form the matrix. The size of the pebbles varies greatly ”