314 Reoieros—Agassiz : Geological Sketches, 



Series," which they prove to be nearly 2,800 feet thick in Yorkshire, 

 with five thick beds of gritstone, — about half of the thickness in 

 Derbyshire, — and only about 300 feet thick, with two gritstone 

 beds, in North Staffordshire. They point out that the topmost of 

 these grits (the ''Kough-rock "), and the third, are continuous 

 throughout ; and that each great grit-bed had a coal-seam on its 

 surface, indicating that, in the intervals, during which the changes, 

 resulting in difference of deposits, were being brought about, each 

 grit-bed became for a time a land-surface. 



II. — Geological Sketches. By L. Agassiz. London, 1866. 

 Tkubneu & Co. 8vo., pp. 311. 



THIS volume contains a series of articles by the well-known 

 Naturalist and Greologist, Professor L. Agassiz, and fi.rst ap- 

 peared in an American periodical, but has since been revised and 

 collected into one volume. 



The contents, originally delivered as popular lectures, embrace 

 some of the leading and more interesting facts of geological science, 

 and are to some extent illustrative of American geology, combined, 

 however, with similar as well as additional phenomena presented by 

 the Old World, with which the author is thoroughly cognizant. 



The varied nature of the lectures will be seen from the following 

 subjects, — America, the Old World, — the Silurian Beach, — the Fern 

 Forests of the Carboniferous Period, — Mountains and their Origin, — 

 the Growth of Continents, — the Secondary and Tertiary Ages, and 

 their characteristic animals ; which are followed by three chapters 

 on a favourite study of the author, — ^viz. : the formation, internal 

 structure, external appearance, and progression of Glaciers. The 

 subject of Glaciers, with which Professor Agassiz is so well acquainted, 

 occupies one-third of the volume, and is treated with special reference 

 to their geological significance, and is to some extQnt introductory to 

 a future work, in wliich the former extension of glaciers in America 

 and Europe — the history of their retreat, and the changes which the 

 climate of our globe has imdergone, will be explained. 



The style of the work is familiar, and fulfils the intention for 

 which the original lectures were published, of placing before the 

 reader some pictures of the Old World, with the animals and plants 

 that have inhabited it at various times, avoiding as far as possible, 

 all debateable ground, embodying those parts of the subject which 

 are best known, and can therefore be more clearly presented. 



Leaving out the Eozoon of the Laurentian rocks, the author has 

 the following suggestive passage in the chapter on the Silurian 

 beach : — "To look on the first land that was ever lifted above the 

 waste of waters, to follow the shore where the earliest animals and 

 plants were created when the thought of God first expressed itself 

 in organic forms, to hold in one's hand a bit of stone from an old 

 sea-beach, hardened into rock thousands of centuries ago, and 

 studded with the beings that once crept upon its surface, or were 



