imaginary, for the record of the rocks tells little or nothing. In face of such an imperfection as this, geologists should surely be humble, and make confession of ignorance to any extent that may be desired. Yet we may at least, with all humility and self-abasement, ask our critics how they know that this great blank really exists, and whether it may not be possible that the swarming life of the early Cambrian may, after all, have appeared suddenly on the stage in some way as yet unknown to us and to them. [20] Walcott and Matthew record more than 160 species of 67 genera, including Sponges, Zoophytes, Echinoderms, Brachiopods, Bivalve and Univalve shellfishes, Trilobites and other Crustaceans from the Lower Cambrian of the United States of America and Canada alone; and these are but a portion of the inhabitants of the early Cambrian seas. There is a rich Scandinavian fauna of the same early date, and in England and Wales, Sailer, Hicks and Lapworth have described many fossils of the basal Cambrian. From year to year, also, discoveries of fossil remains are being made, both in America and Europe, in beds of older date than those previously known to be fossiliferous. At present, however, these remains are still few and imperfectly known, and it is not in all cases certain whether the beds in which they occur are pre-Cambrian or belong to the lowest members of that great system. It is unfortunate that so many of the strata between the Laurentian and the Cambrian seem to be of a character little likely to contain fossils; being littoral deposits produced in times of much physical disturbance. Yet there must have been contemporaneous beds of a different character, which may yet be discovered. References:--"Fossil Sponges from the Quebec Group of Little Metis, Lower St. Lawrence": _Transactions Royal Society of Canada_, 1890. "Rèsumè of the Carboniferous Land Shells of North America": _American Journal of Science_, 1880. "Burrows and Tracks of Invertebrate Animals": _Journal Geological Society of London_, 1890. "Notes on the Pleistocene of Canada": _Canadian Naturalist_, 1876. "Air-breathers of the Coal Period ": _Ibid._, 1863. _THE HISTORY OF THE NORTH ATLANTIC._ DEDICATED TO THE MEMORY OF PROF. JOHN PHILLIPS, OF OXFORD, One of the most able, earnest, and genial of English Geologists; and of other Eminent Scientific Men, now passed away, who supported him as President of the British Association, at its Meeting in Birmingham, in 1865. Distribution of Land and Water--Causes of Irregularities of the Surface Crust and Interior--Position of Continents--Past History of the Atlantic--Its Relations to Life--Its Future [Illustration: Map of the North Atlantic, showing depths from 4,000 fathoms upward (after the Challenger Survey).] CHAPTER IV.