. An introduction to geology : intended to convey a practical knowledge of the science, and comprising the most important recent discoveries, with explanations of the facts and phenomena which serve to confirm or invalidate various geological theories. clay with sandstone. ^ This may be regarded as a localb Sandstone, calcareous grit. ! formation of limited extent,c Petworth and Purbeck lime- ( but extremely interesting onstone. J account of its fossil remains. 5. Green Sand and Chalk. a Lower green sand and ironsand. b Blue clay, called Gait,c Upper green Chalk Chalk wiihout fli
. An introduction to geology : intended to convey a practical knowledge of the science, and comprising the most important recent discoveries, with explanations of the facts and phenomena which serve to confirm or invalidate various geological theories. clay with sandstone. ^ This may be regarded as a localb Sandstone, calcareous grit. ! formation of limited extent,c Petworth and Purbeck lime- ( but extremely interesting onstone. J account of its fossil remains. 5. Green Sand and Chalk. a Lower green sand and ironsand. b Blue clay, called Gait,c Upper green Chalk Chalk wiihout Upper or flinty chalk. Calcaires oolitiques, and some-times calcaires de Jura, andalso calcaire Alpin. Gres vert et gres ferrugineux, Craie inferieure, etCraie superieure. introduce numerous subdivisions of strata, and to identify them with those in othersituations, will be ready to acknowledge that such labours are too microfogical,and that by endeavouring to mark divisions, where Nature has not establishedthem, we lose our time, and introduce needless perplexity into the science. Areference to the two sections of the oolite formation, given at the end of the nextchapter, will serve to evince the truth of the above NEW RED SANDSTONE. 161 New Red Sandstone is so called to distinguish it from a red sand-stone found among transition rocks, (See Chap. VII.) The new redsandstone is a very extensive and complex formation : its prevailingmineral character is siliceous ; but it sometimes comprises calcareousbeds of considerable magnitude and extent. The new red sandstonemay be conveniently divided into three series, or the upper, the mid-dle, and the lower beds; where the beds of limestone occur, theyserve to mark the divisions in the series with sufficient distinctness,but where they are wanting, these divisions cannot always be observ-ed. A limestone containing magnesia, separates the lower from themiddle series, in the northern counties of England, but
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