HARDWICKE'S S OIKN CE-GOSSIP. 



275 



To tliis day, in the iieiglibouiliood of Scarborough 

 £P.d Whitby, the fossil Ammoniles which are so 

 abundant and characteristic in the Lias and lower 

 Oolitic formations, go by the name of "Snake- 

 stones," or " Petrified Snakes." You may see them 

 in the lapidaries' shops named as such, and not uu- 

 iVequently having casts of snakes' heads attached to 

 them— the latter being a "restoration," perhaps. 



Fig. I89. Ammonites commiiiiin. 



Fig-. 190. Side view. 



on a par with '," restorations " generally ! The 

 commonest species selected for this purpose are 

 Aiiimonites annulatm or A. communis, ■whose closely 

 ringed whorls strongly resemble coiled-up snakes — 

 hence the legend. 



What are these common and beautiful fossils ? 

 There are no fewer than five hundred species known 

 to geologists, ranging, in geological time, from the 

 Lias to the Chalk formations inclusive. Few fossils 

 are more beautiful, each species having a distinct 

 ornametttation, and, perhaps, even each stage of 



will have seen, are straight and simple along their 

 edges, and the siphuncle, or air-tube, runs down 

 the centre of each chamber, and connects them all 

 together. 



The Ammonites were first cousins to the Nautilus. 

 Before their appearance in the seas of the Liassic 

 epoch, their place had been occupied by a kindred 

 group, called Ceratites. Instead of having the 

 chambers straight, however, the Ammonites had 

 theirs foliated or serrated very ornately and com- 

 plexly along their edges. In the Goniatites, -which 

 abound in the carboniferous limestone, these cham- 

 bers are angled— hence the name of the genu.s. In 

 the Ceratites, which are characteristic of the Trias 

 formation, the edges of the chambers are foliated, 

 but not so intricately as in the Ammonites, whilst 

 that part which projected towards the mouth of the 

 shell was tolerably simple. It is a significant fact 

 that the young Ammonites greatly resemble the 

 Ceratites, losing this resemblance as they got older. 

 The geographical distribution of the Ammonites 

 is very great. They are found in the secondary 

 rocks of Europe, South Africa, America, India, and 

 the West Indies. 



Fig. 191 . Ammonites o/itimtis. Fig. 192. Side view. 



individual growth. Their name of Ammonite is 

 derived from the Cornu Ammoius, or " Jupiter - 

 Amnion's" horn, by which they were known among 

 the ■virtuosi of a century ago. Their natural history 

 relations, however, are with the Nautilus, which 

 beautiful family is now approaching extinction, 

 having been in existence since Silurian times. The 

 chambers of the common Nautilus, as our readers 



Fig. 193. Ammonites hifrons. 



Fig. 194. Side view of ditto. 



At present a good deal of artificial arrangement 

 exists among these interesting fossils, and it is 

 known that different species have been so classed 

 which arc really nothing but the distinct and various 

 stages of marked individual growth. They arc 

 roughly divided into six groups, as follows : — 1. The 

 back marked by an entire keel ; 2. Back crenated ; 

 3. Back sharp ; 4. Back channelled ; 5. Back 

 squared ; and 6. the back round or convex. 



The largest of these "Snake-stones" occur in tlie 



