A DAY IN A QUARRY. 93 



technically Brachiopoda. They differ from the more 

 ordinary types of bivalves, such as mussels, oysters, 

 etc. (Lamellibranchiata), in being always equal-sided 

 and never quite equivalvular i.e., the two shells 

 are symmetrical, but not of equal size. The old 

 naturalists called them lampades, or lamp-shells, 

 from their fancied resemblance to the antique lamps 

 of symmetrical form, whose wick corresponded to 

 the pedicle, or footstalk, by which the creature in a 

 later stage of development attaches itself to some 

 submarine object. 



After some further talk about our specimens, we 

 resumed our hunt. Baxter stopped me in a moment 

 or two, however, by saying, " I am not quite clear 

 about the way in which these rocks, which, you say, 

 were formed at the bottom of the sea, have become 

 elevated and removed so far from the ocean. I 

 have been puzzling over that problem ever since 

 we got into the quarry. Do you think you could 

 explain it a little more simply for my dull com- 

 prehension ? " 



" It is probable," I replied, " that volcanic agency 

 had a great deal to do with the matter in this 

 particular place. If you will just step up here 

 where I have been at work, you will get a tolerably 

 good view of the surrounding district, and you will 

 perhaps be able to make out that it is roughly conical. 

 Sir Roderick Murchison, whose magnificent work 

 Siluria is by far the best geological guide for 

 this part of the country, is of opinion that this 

 locality forms the crater of a gigantic extinct volcano, 

 which has been worn down by the action of water 



