Shaler.] 



128 [February 15, 



are so porous that water runs through them as it does 

 through sand. The natives are obliged to place calabashes 

 to catch the rain. Water which is filtered through the roofs 

 of the caverns is perfectly pure. 



Dr. Chas. T. Jackson referred to Etna as another instance 

 of a volcano which does not overflow its crater. The lava 

 breaks its way down by Monte Rosa. The openings of the cra- 

 ter of the volcano on the Island of Ischia also, is not at the 

 summit but on the side of the mountain, and at Stromboli, 

 visitors can stand on a table rock above the crater, while ex- 

 plosions are taking place every minute. 



Mr. "W". H. Niles spoke of an examination recently made 

 by him of a quarry of the sandstone series at Montague, and 

 referred to the extremely large size of the conglomerate 

 pebbles found in that vicinity. He also exhibited specimens 

 to illustrate the lateral change in a bed of conglomerate, at 

 the Chestnut Hill Reservoir, Brighton, Mass. He showed 

 pebbles of quartz, or of quartzose rock, from the conglomer- 

 ate, which were from two to five inches in diameter, and not 

 larger than many others there ; only fifty-eight feet from these 

 pebbles when in the rock, the same stratum was entirely 

 a fine argillaceous slate, a specimen of which was shown. 

 Also specimens of the intermediate rock were used to illus- 

 trate the nature of the change. 



Dr. Pickering said that the conglomerate appears in almost 

 every part of the globe. He had found it in the Pacific Is- 

 lands, but he had seen it containing boulders, like that de- 

 scribed by Prof. Mies, only on the Island of Madeira. In 

 regard to the formation of conglomerate, he said we do not 

 want the aid of sea or river, but only to conceive of the re- 

 cent deposits, which we see about Boston, hardening into 

 rock. He had tried in vain to find the conglomerate at Ha- 

 waii; the lava is amorphous and insoluble. 



