in each of the principal groups of fragmental rocks we must recognize an unconsolidated division and a consolidated division. (1) _Conglomerate group._—The rocks belonging in this group we know before consolidation as _gravel_, and after consolidation as _conglomerate_. Gravel.—The pebbles, as we have already seen, are usually, though not always, well rounded or water-worn; and they may be of any size from coarse grains of sand to boulders. As a rule, however, the larger pebbles, especially, are of approximately uniform size in the same bed or layer of gravel, with, of course, sufficient fine material to fill the interstices. Although the same limited mass of gravel may show the widest possible range in chemical and mineralogical composition, yet hard rocks are evidently more likely than soft rocks to form pebbles; and hence quartz and quartz-bearing rocks usually predominate in gravels. Specimen 28. Conglomerate.—Consolidated gravel. Children should be led to an appreciation of this point by a careful comparison of the forms of the pebbles in the gravel and conglomerate. The conglomerate seems to contain a larger proportion of fine material than ordinary gravel. But this is because the gravel is usually, as with our specimen, taken from the _surface_ of the beach, where, of course, the pebbles are clean and separate; but if it had remained there to be covered by a subsequently deposited layer, enough fine stuff would have been sifted into the holes to fill them. And in the finished gravel, just as in the conglomerate, the pebbles are usually closely packed, with just sufficient sand and clay, or _paste_, as the material in which the pebbles are imbedded is called, to fill the interstices. The paste is usually similar in composition to the pebbles, with this difference: hard materials predominate in the pebbles and soft in the paste. Stratified rocks generally show the stratification in parallel lines or bands differing in color, composition, etc.; but nothing like this can be detected in our specimens of conglomerate; and the question might be asked, How do we know that this is a stratified rock? In answer, it can be said that our hand-specimens appear unstratified simply because the rock is so coarse; but when we look at large masses, and especially when we see it in place in the quarry, that parallel arrangement of the material which we call stratification is usually very evident; and we often see precisely the same thing in gravel banks. It is, however, wholly unnecessary that we should _see_ the stratification in order to know certainly that this is a stratified or aqueous rock, because the forms of the pebbles show very plainly that they have been fashioned and deposited by moving water; and we have in the smallest specimen proof positive that our conglomerate is a consolidated sea-beach.