220 



SCIENTIFIC NEWS. 



[Sept. 7, i? 



denudation, and by this process other rocks were 

 originated. 



The sub-systems of the Mesozoic Period, with which 

 this article is concerned, are the Permian, Trias, and 

 Jurassic. The Permians form a debatable ground be- 

 tween the Carboniferous and Trias, but into the merits 

 of the arguments we need not enter. 



The Trias formation as typically developed on the 

 Continent of Europe, consists of the following divi- 

 sions :— 



3. Keuper. 



2. Muschelkalk. 



1. Bunter. 



In England the Muschelkalk has not been clearly 

 proved to be represented, but we have the equivalents 

 of the Bunter and Keuper. The Bunter series are not 

 developed in the neighbourhood of Bath, but there are 

 some beds which may correspond with the Keuper, and 

 these are of considerable interest. They are locally 

 known as the Dolomite or Magnesian Conglomerate, 

 so-called from dolomite (carbonate of lime and magnesia) 

 forming a cementing matrix, by which the boulders and 

 pebbles which occur in the rock are held together. The 

 Dolomitic Conglomerate may be seen to advantage at 

 Clifton, on the left-hand side of the " New Road " leading 

 from Clifton to the Hot Wells* 



Among the varied life of the Trias Period reptiles 

 were very abundant, which, indeed, is a feature of the 

 secondary strata, and hence it has sometimes been called 

 the " Age of Reptiles." 



The only inference that can be drawn from the blocks 

 of Carboniferous limestone constituting the Conglomerate 

 is, that the limestone must have undergone denudation. 

 The Dolomitic Conglomerate is probably a consolidated 

 beach ; if we compare its appearance with what we see 

 on the beaches around our coasts and islands, the 

 similarity is at once apparent. Sir H. De la Beche says, 

 in reference to the origin of the conglomerate, " Stand- 

 ing on any high ground or the Mendip Hills, it is in- 

 teresting to consider how exactly the masses occur as 

 they should do, under the supposition that they have been 

 beaches among islands, raised above the sea of the times." 



The Trias period is also represented by the New 

 Red Marl, which, however, is not of much interest. 

 The various localities at which it is exposed may be 

 readily seen by reference to the Geological Survey map 

 of the district around Bath. The Trias period was 

 brought to a close by the formation of a series of beds, 

 known on the Continent as the Rhcetic. The equivalent 

 strata in this country are typically represented at Penarth 

 near Cardiff, and they are therefore sometimes known as 

 the Penarth Beds. In England they occupy the position of 

 passage beds between the Trias and Lias formations. 



At the base of the Rhcetic beds in this country we 

 get a series of green and red marls, which represent 

 the last of the Trias rocks. Then a well-marked physical 

 change is indicated by a very interesting bed, in which 

 the shell Avicula contorta is numerous, and this suggested 

 to Dr. Wright that it should be called the Avicula contorta 

 bed. Then follow black shales in one of which, the 

 " Bone Bed," fish and reptilian remains are especially 

 abundant. Then another change is indicated by a cream- 

 coloured limestone, named by William Smith, in 1815, 

 the White Lias. Now, the Avicula contorta zone and the 

 White Lias are well-defined geological landmarks, and 



* The Dolomite Conglomerate is also well shown at Tytherington. 



hence Mr. Charles Moore* has included in the Rhcetic 

 series the strata between those two horizons. 



Near the base of the White Lias is a well-known 

 ornamental limestone, known as the " Landscape 

 Marble," which is about one foot thick. One of the 

 best exposures of the White Lias is to be seen just out- 

 side Bath, near the Weston station on the Midland 

 Railway. 



We now enter upon the Jurassic rock, on which Bath 

 rests, and of which the hills surrounding the city 

 are built up. The Jurassic period of the earth's history 

 is typically represented in the Jura Mountains, and hence 

 the name Jurassic. In this country there are two dis- 

 tinctive series, namely, the Lias and Oolitic. It is the for- 

 mer of these which overlie the White Lias of the Rhcetic, 

 and are clearly distinguished by the blue colour of the 

 limestone, and dark intervening shales. According to 

 Sir H. De la Beche, the term Lias originated with the 

 Somersetshire quarrymen, and by them was applied to 

 distinguish argillaceous limestone forming a part of the 

 succession of strata now all included under the name. 

 Of the reptiles which inhabited the Lias seas, estuaries, 

 rivers, and land we have some most wonderful combina- 

 tions of structure. Three groups are found — the Ena- 

 liosaurians, or marine reptiles, the Pterodactylians, or 

 aerial reptiles, and the Tcleosaurians, or river and land rep- 

 tiles. 



The most prominent group are the Enaliosaurs, or Sea- 

 Lizards, the two groups of which are represented respec- 

 tively by the Ichthyosaurus and Plesiosaurus. Good 

 specimens may be seen in the Bath Museum, and some of 

 the best ever obtained have been found in the Lower 

 Lias of Street in Somersetshire. The Ichthyosaurus was 

 indeed a wonderful creature. In size it was sometimes 

 as much as 24 feet in length ; it had the skull of a crocodile, 

 the eye fashioned like a bird and a turtle. It had the 

 backbone of a fish, the paddle of a whale, and the 

 scapular arch of a Platypus. 



The Plesiosaurus was hardly less remarkable. It was 

 distinguished by its long neck, resembling that of a 

 swan united to the trunk of a quadruped, with ribs like 

 a chameleon. 



There is another reptile that appears for the first time 

 in the Lias, which has a unique history, seeing that 

 nothing approaching to it is found either in living or ex- 

 tinct natural forms. This is the Pterodactyle, a flying 

 reptile, whose skeleton was modified and adapted to an 

 aerial life. It had some resemblance to bats and birds, 

 but was widely different from both. In bats the whole 

 anterior extremity is elongated to form a framework of a 

 wing, but in the Pterodactyle it was only the little finger 

 that was lengthened and strengthened to become a rod 

 for supporting a membrane, whilst the other parts of the 

 hand, the thumb, and three inner fingers retain their 

 normal size. Like birds, the long bones of the arm 

 were hollow cylinders, and it differed from birds in 

 having the skull of Reptilia. Its jaws were armed with 

 long teeth implanted in distinct sockets. 



The Teleosaurians, or land reptiles, appear in the Upper 

 Lias. Several examples of small specimens have been 

 found in the fish-bed of Dumbledon, and in the same 

 formation in Somersetshire as well as in Yorkshire. 



English geologists divide the Lias, as represented in this 

 country, into three divisions, namely, Lower, Upper, and 

 Middle, and each one is marked by palasontological 



* " Quart. Jour. Geol. Soc," vol. xvii., p. 495, l85l. 



