DEEP-SEA DREDGING AND GEOLOGICAL AGE.
To TUB EDITOR OF THE "SPROTITOR:1 SIR,—Allow me to point out what appears to me to be an error in the otherwise excellent article on "Deep-Sea Dredging" which appeared in your last issue. The writer says, "If there is one theory which geologists have more justly formed than all others, it is the view that the various strata of the earth were formed at different times. A chalk district, for example, lying side by side with a sandstone district, has been referred to a totally different era Now, however, Dr. Carpenter and Professor Thompson may fairly be said to have changed all this." In this paragraph the writer has understated the case. No geologist would think of saying, that simply because a rock here was chalk and one over the way was sandstone, each was of a different age to the other, unless one was superimposed on the other. Indeed, if there is one word in more frequent use than another among geologists, it is "equivalent," as used in reference to rocks which, deposited con- temporaneously, yet differ as widely from each other as sandstone and chalk. What, for example, can present a greater divergence in chemical composition and general appearance than does the Wenlock shale in Denbighshire from that of the adjoining county of Salop? If the bottom of the ocean now presented the anomalous appearance of a succession of beds, one on the top of the other, yet all deposited at the same time, then the researches of Dr. Carpenter and Professor Thompson would, indeed, upset the theories of geologists, and the theories of a good many people besides. As it is, the change in the sediment they have observed within the distanee of a few miles, is just that common change which geologists so often describe as occurring in the same bed of rock within
-.distances equally small.—I am, Sir, &c., D. C. D.
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