If it be asked what has become of the supposed matrix in which these flints were formed, and how could strata so considerable as they must have been, have disappeared without leaving a single trace of their existence? It may be answered, that the difficulty is exactly the same in supposing them to be derived from the chalk; for no remains of this rock are to be found with these pebbles; and it is equally impossible to discover what has become of the chalk that must have belonged to the flint pebbles that are undoubtedly derived from it.
But when we see rolled pieces of granite, of quartz, and other primitive rocks, occurring frequently in the alluvium of this part of the country, though so far removed from the places where these substances are in situ, we feel so assured of the extensive nature and violent action of the cause that has occasioned such destruction, that we need not wonder if many strata have been reduced to a state of impalpable division, and have been scattered over the surface, so that not a fragment remains entire; or have been deposited in the depths of the ocean, where they may have formed new combinations that may at some distant period be exposed to view, and afford matter for the contemplation of future generations. The Hertfordshire pudding-stone has been already mentioned. It is composed of these concentric pebbles united by a granular quartz, and is most abundant in the neighbourhood of St. Alban's, but is found in many other places above the chalk. It occurs in large irregular masses in the gravel; but I am not aware that it exists any where in an extensive bed in situ.
To account for the appearance of this pudding-stone we have to suppose, 1st, the existence of a stratum superior to the chalk, containing under some form, the substance of which these pebbles are composed. 2d, the agency of some power capable of breaking
