No. 136.] ' 11 



layers of black limestone; the upper part, often calle4 the I 



Oolite, is generally yellowish or drab limestones and shales. 

 The Lias abounds in shells of numerous genera : among the most 

 abundant are the Ammonites, or nautilus-like chambered shells 

 with curiously plicated partitions. Of these, there are in the 

 Lias and Oolite, and the Chalk which overlies them, more than a 

 thousand species, many of them very beautiful and graceful in 

 form, and varying in size from that of a dime to four feet 

 diameter. Many kinds of fishes are found in the Lias, some of 

 them so well preserved that hardly a scale is out of place ; but 

 instead of the strange heavily-plated fish of the Devonian system, 

 they approach in form more nearly to existing fishes. There are 

 fossil plants, all differing from those of the Coal formation. The 

 most remarkable of the remains in the Lias, however, are those 

 of reptiles ; many of which are larger than any now known, and 

 of very strange forms, seeming to blend the characters of reptiles 

 with those of fishes ; and there is one very remarkable family of 

 small reptiles (the Pterodactyles), which had bat-like wings, 

 seeming to realize the fables of flying dragons. 



The Oolites, or upper Jurassic strata, contain many beautiful 

 Echini, or Sea-eggs and reptiles, fish and shells in great num- 

 bers ; but the most important relics found in them are those of 

 the earliest known Mammalia.* These seem to have been small 

 quadrupeds allied to the Opossum, and belonging to the lowest 

 orders of the Mammalia ; but they mark, so far as is yet known, 

 the first appearance of any terrestrial or warmblooded animals 

 except birds. Remains of Insects are also found in some Jurassic 

 layers, the fine texture of which (in the Lithographic limestone 

 of Bavaria) admitted of the perfect preservation of such fragile 

 things. 



The Jurassic is succeeded by the Cretaceous system, of which 

 the White chalk forms in England and France a considerable 

 portion, being several hundred feet thick where seen in the sea- 

 side precipices of Beachy Head and Dover. The whole system 

 abounds in fossils, consisting of fish, reptiles, shells of many 

 families, echini, crinoids, etc. etc. One of the most remarkable 

 evidences of the quantity of the smallest forms of life which 

 have existed, is found in the fact that a great part of this enor- 



* Mammalia are animals i^hich nurse their young j a great class, comprehending all the 

 more highlyorganized animals. 



