. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 98 CHRONOLOGICAL ARRANGEMENT [Ch. IX. sented to tlie reader, as laid down on a true scale by Prof. Ramsay, where the newer groups 1,2, 3,4, rest uncomformably on the formations Fig. 103. Dundry Section South of Bristol. Length of section, 4 miles. a, b. Level of the sea. 1. Inferior oolite. 2. Lias. 3. New red sandstone. 4. Magnesian conglomerate. A. C. Kamsay. 5. Coal measures. 6. Carboniferous limestone. 7. Old red sandstone. 5 and 6. Here at the southern en
. Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments. Geology. 98 CHRONOLOGICAL ARRANGEMENT [Ch. IX. sented to tlie reader, as laid down on a true scale by Prof. Ramsay, where the newer groups 1,2, 3,4, rest uncomformably on the formations Fig. 103. Dundry Section South of Bristol. Length of section, 4 miles. a, b. Level of the sea. 1. Inferior oolite. 2. Lias. 3. New red sandstone. 4. Magnesian conglomerate. A. C. Kamsay. 5. Coal measures. 6. Carboniferous limestone. 7. Old red sandstone. 5 and 6. Here at the southern end of the line of section we meet with the beds No. 3 (the New Red Sandstone) resting immediately on No. 6, while farther north, as at Dundry Hill, we behold six groups superim- posed one upon the other, comprising all the strata from the inferior oolite to the coal and carboniferous limestone. The limited extension of the groups 1 and 2 is owing to denudation, as these formations end ab- ruptly, and have left outlying patches to attest the fact of their having originally covered a much wider area. In many instances, however, the entire absence of one or more forma- tions of intervening periods between two groups, such as 3 and 5 in the same section, arises, not from the destruction of what once existed, but because no strata of an intermediate age were ever deposited on the in- ferior rock. They wrere not formed at that place, either because the region was dry land during the interval, or because it was part of a sea or lake to which no sediment was carried. In order, therefore, to establish a chronological succession of fossilifer- ous groups, a geologist must begin with a single section, in which sev- eral sets of strata lie one upon the other. He must then trace these formations, by attention to their mineral character and fossils, continu- ously, as far as possible, from the starting point. As often as he meets with new groups, he must ascertain by superposition their age r
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