384 



THE CARBONIFEROUS SYSTEM. 



other known species of its race, there being, with the exception of the 

 next species, no other Pulmonate known until we reach the Purbeck 

 beds, and no other true land snail until we reach the Tertiary, 



Fig. 149. — Pujpa Vetusta, Dawson. 



(a) Natural size. 



(b) Enlarged. 



(c) Apex enlarged. 



(d) Sculpture; magnified. 



In the section of the South Joggins I have noticed the occurrence 

 of Pupa Vetusta in another bed 1217 feet below that above mentioned. 

 It belongs to group 8 of the section, and is between coals 37 and 38 

 of Logan's sectional list. It is a layer of gray indurated clay, with a 

 slightly nodular structure, and in some places becoming black and 

 carbonaceous, and containing leaflets of ferns, Trigonocarpa, etc. The 

 shells occur very abundantly in a thickness of about two inches. They 

 have been imbedded entire ; but most of them have been crushed and 

 flattened by pressure. They occur in all stages of growth ; the young 

 being, as is always the case in such shells, very different in general 

 form from the adults. This bed is evidently a layer of mud deposited 

 in a pond or creek, or at the mouth of a small stream in shallow water. 

 In modem swamps multitudes of shells occur in such places ; and it 

 is remarkable that in this case land shells should alone be found, 

 without any trace of aquatic molluscs. The shells which occur in 

 this bed are filled with the surrounding sediment. Those which occur 

 in the erect SigillaricB, on the other hand, except when they are 

 crushed and flattened, are filled with a deposit of brown calc-spar. I 

 infer from this that the latter, when buried, contained the animals, and 

 consequently that these lived or sheltered themselves in the hollow 

 trees, as is the habit of many modern land snails. 



