65 



shaft now being worked is fifty feet. The coal is columnar 

 and loose, so that it cannot be worked in the usual way by 

 undermining it, but it is taken out by means of a series of hori* 

 zontal grades. It requires no blasting, but can be easily de- 

 tached with the pick. This mine affords evidence that the strata 

 were once horizontal. Black and white Gypsum are found in 

 the neighboring rocks. 



The strata adjoining the coal beds are a very fine-grained 

 shale. They contain rounded masses like pebbles, principally 

 made up of scales of ganoid fishes, which must have been formed 

 by eddies and whirls in the water. Ripple marks are also found. 

 These shales must have been formed from very fine mud, such as 

 can only be deposited by very calm water. 



Dr. Jackson was so fortunate as to obtain specimens of two 

 species of ganoid fishes from this rock, one of them nearly per- 

 fect, which he exhibited to the Society. The specimen also 

 showed traces of fossil plants. 



Dr. Jackson stated, that in the vicinity of the coal deposit very 

 numerous specimens of fossil trees, such as Stigmaria, Sigillaria, 

 &c. of great size are found. 



Prof. Wyman mentioned some facts which had come 

 under his observation relating to the development of Disto- 

 mata. 



He remarked, that in dissecting tadpoles, which were hatched 

 during the last summer, but had remained through the winter 

 without undergoing their metamorphosis, he had found them 

 infected with great numbers of Distomata, situated within the 

 peritoneal cavity, in the muscular tissues, and beneath the skin. 

 They were most abundant in the latter position, at the junction 

 of the tail with the body, and in most instances were surrounded 

 by a cyst, except in the peritoneum, where they were for the 

 most part free. 



The Distoma is interesting as exhibiting one of the phases of 

 an alternation of generations, being produced by Cercaria, which 

 has been traced by Steenstrup to a " nurse " and a " grand 

 nurse. '^ Thus, four generations at least are required for the 

 development of a Distoma. 



The development of the pelvis of the tadpole presents some 



PEOCEEDINGS B. S. N. H. 5 AUGUST, 1851. 



