1835.] the Advancement of Science. 191 



the fossil species of the present genus did not afford results 

 very favourable to such a hypothesis. Confining our atten- 

 tion to the oolite and lias, it was observed that one species 

 of Astacus was found in every bed, from the lowest of the 

 lias to the uppermost of the oolite. 



One species was confined to the coral rag ; four species 

 were peculiar to the green sand ; some of the species were 

 more local, and others appear to have had a wider geogra- 

 phical distribution, as is the case with the Astaci of the 

 present day. 



Mr. Grifi^ith then resumed the explanation of his Geolo- 

 gical Map, and described the erupted rocks which have 

 been observed in Ireland. He divided the unstratified 

 masses into three portions : 1. Those occurring in transi- 

 tion and primary rocks : 2. In the older secondary : 3. In 

 the newer secondary. 



It was remarked that the limestone which comes in con- 

 tact with the erupted rocks of the primary division, is often 

 changed into dolomite. 



Green stones occur among the older secondary rocks in 

 the county of Limerick. These green stone beds are appar- 

 ently interstratified with the lime-stone, but fragments of 

 this latter rock are included in the trap. 



The trap veins occurring in the newer secondary for- 

 mations, as in the chalk of Antrim, are already sufficiently 

 well known. Mr. G. is of opinion that the porphyry of 

 Sandy rock is merely a modification of the ochre beds which 

 are observed at the Giants Causeway, as there is a striking 

 resemblance between the two rocks, in point of mineral 

 character, and both contain nodules of mesotype. 



Wednesday^ \2th. — Mr. Griffith gave anaccount of amass 

 of shelly gravel in the county of Wexford : this deposition is 

 very extensive, stretching along the coast for a distance of 

 seventy miles, and attaining a breadth of eighteen. The 

 following is a section of this deposit : 



5 feet of clay 



7 feet marl clay 



7 feet marl 



7 feet of sand 

 11 feet of gravel, containing abundance of marine shells. 



5. Mr. Phillips then read a paper on the genus Belemnite. 



