The celebrated statuary marbles of Carrara, which have of late I years been universally described as of Jurassic age, have quite recently been shown conclusively to belong to the Carboniferous series, and the steps which have led to the discovery form an instructive illustration of the difficulties which beset Alpine Geology. No one has a better right to relate the history of the classification of the rocks of the Apuan Alps than M. Coquand, and this he is now doing in a series of papers published in the Bulletin of the Geological Society of France. From the first of these we arrive at the following résumé of the various opinions which have been held-from time to time regarding the age of the statuary marbles.

Just a year ago the Academy received information that the day before there had fallen at Haga (a royal residence in the neighbourhood of Stockholm) rain mixed with snow, which brought down with it such a quantity of impurities that all the windows of the plant-house and the hot-beds there were covered with a fine grey ash-like dust.

It has long appeared to me that much remains to be said on this subject. When Mr. Croll's papers on the Physical Cause of the Motion of Glaciers appeared in the Philosophical Magazine for March, 1869, and September, 1870, I felt that, though his theory was certainly ingenious, and his statement of it clear and masterly, these papers were far from affording a satisfactory solution of the problem of which they treated. I waited, fully expecting that Mr. Croll would supplement and modify his theory, but he has not done so to my knowledge. Geologists in general seem to be as satisfied with it as he is himself, and on all hands they appeal to it as supporting them, whenever they treat of glacial phenomena, even when, if true, it shows their theories to be vain. A rather conspicuous instance of this occurs in the Geol. Mag. for October of last year, in an interesting paper by Mr. Goodchild on Coums. In that paper Mr. Goodchild commends “a proper appreciation of Mr. Croll's theory”; but I am persuaded that a proper understanding of it would have caused him either to renounce that theory or his own on the origin of Coums. I have thought it time, therefore, to place on these pages my criticisms and difficulties for the consideration of geologists, even if, as is unfortunately too likely, I have little new to advance.

1. Succession of Silurian Rocks in the South of Scotland.—The oldest fossiliferous strata yet detected in the Silurian district of the South of Scotland are the dark Graptolitic shales forming the well-known Moffat Series. The total thickness of this group is under 600 feet, but it is nevertheless capable of separation into three very distinct palæontological divisions, each characterized by a large proportion of peculiar fossils. The first of these divisions is of Llandeilo age, the second represents a portion of the Bala formation of North Wales, and the third, or Birkhill division, appertains, at least in part, to the epoch of the Lower Llandovery.