No remains, however, of them or of any vertebrate animal have yet been discovered in the ordovician strata, rich as these are in invertebrate fossils, nor in the still older Cambrian; so that we seem authorised to conclude, though not without considerable reserve, that the vertebrate type was extremely scarce, if not wholly wanting, in those epochs often spoken of as "primitive," but which, if the Development Theory be true, were probably the last of a long series of antecedent ages in which living beings flourished.
"The Antiquity of Man"
Charles Lyell
Nearly the entire Himalaya east of Kashmir became a land surface and remained exposed to denudative forces for so long a time that in places the whole of the Carboniferous, Devonian, and a large part of the Silurian and ordovician deposits were removed-some thousands of feet in thickness-before resubmergence in the Tethys occurred.
"The Birth-Time of the World and Other Scientific Essays"
J. (John) Joly
The Cambrian carries the Roman name of Wales, and the ordovician and Silurian the names of tribes of ancient Britons which inhabited the same country.
"The Elements of Geology"
William Harmon Norton