There is perhaps no problem at once so difficult and so full of interest to the student of the Earth’s history, as the interpretation of the fragmentary records of the opening stages in geological and organic evolution. In tracing the growth and development of the human race, it becomes increasingly difficult to discover and decipher written documents as we penetrate farther back towards the beginning of the historical period; the records are usually incomplete and fragmentary, or rendered illegible by the superposed writings of a later date. So in the records of the rocks, as we pass beyond the oldest strata in which clearly preserved fossils are met with, we come to older rocks which afford either no data as to the period in which they were formed, or like the palimpsest, with its original characters almost obliterated by a late MS., the older portions of the Earth’s crust have been used and re-used in the rock-building of later ages. In the first place, it is exceedingly difficult to determine with any certainty what rocks may be regarded as trustworthy fragments of a primaeval land. Throughout the geological eras the Earth’s surface has been subjected to foldings and wrinklings, volcanic activity has been almost unceasing, and there is abundant evidence to show how the original characters of both igneous and sedimentary rocks may be entirely effaced by the operation of chemical and physical forces. It was formerly held that coarsely crystalline rocks such as granite are the oldest portions of the crust, but modern geology has conclusively proved that many of the so-called fundamental masses of rock are merely piles of ancient sediments which have been subjected to the repeated operation of powerful physical and chemical forces, and have undergone a complete rearrangement of their substance. As the result of more detailed investigations, many regions formerly supposed to consist of the foundation stones of the Earth’s crust, are now known to have been centres of volcanic disturbance and widespread metamorphism, and to be made up of post-archaean rocks. [Sidenote: THE OLDEST ROCKS.]