188 * Scientific Geology. 



quartz, and the cement a black compact substance, highly bituminous, 

 and slightly effervescing with acids. It appears like bituminous 

 marlite, finely comminuted. As already mentioned, in one piece I 

 found the remains of a Zoophyte. 



At the foot of the cliff, I also found rolled pieces of yellowish gray 

 rock, hard and compact, approaching hornstone. It appears like 

 argillaceous sandstone, which has been subjected to powerful heat by 

 the proximity of trap, such as occurs at Mount Holyoke, on Connec- 

 ticut river ; but I have met with the like rock nowhere else in the 

 State. (No. 81.) 



In a kind of ferruginous sand in this cliff, I met with one or two 

 small specimens of a rock of oolitic aspect ; (No. 80.) which, how- 

 ever, effervesces but feebly with the acids. 



Specimens of all the preceding varieties of clay, sand, lignite, and 

 conglomerate, will be found in the collection made for the Govern- 

 ment. 



Mineral Contents. 



The most interesting and abundant mineral at Gay Head, is the 

 hydrate of iron. The varieties are all argillaceous. The most im- 

 portant are the following. 



1. Nodular. This is the most abundant variety, and the nodules 

 vary in size, from that of a walnut to a foot in diameter. Sometimes 

 they are spherical, more frequently ovoid; sometimes ovoid flattened; 

 sometimes composed of concentive layers of the compact oxide and 

 yellow ochre, with a nucleus sometimes of sandstone at the center, 

 but more frequently hollow. These nodules are generally mixed 

 with a large proportion of coarse sand and gravel, which unitedly 

 form, as already remarked, a conglomerate. The flat nodules are 

 sometimes slaty : and it is on the laminae of these, that the principal 

 part of the vegetable remains of this formation occur. Sometimes 

 the nodule, when broken open, is seen to envelope a flattened mass of 

 lignite : showing conclusively that the ore originally accumulated 

 around this as a nucleus. 



Nodular argillaceous iron ore exists also on Nantucket ; as well 

 as in other places on the Vineyard. 



2. Columnar. Some of the larger nodules mentioned above, being 

 broken open, exhibit, as the result of desiccation, a columnar struc- 

 ture in the interior : the columns varying in diameter from a quarter 

 of an inch, to one, and even two inches ; and in length, from half an 



