- 
244 Geology of Martha’s Vineyard. 
grounds are, geologists will place that degree of confidence in 
the opinions advanced. which they consider them as de- 
serving. Besides it must be recollected, that this paper 
does not profess to give a finished sketch of the regions it 
embraces, but only to furnish hints towards their geology. 
diluvial bowlders, occurring along the south-east+ 
ern coast of Massachusetts, are often in immense quanti- 
ties; and of a character, very similar to those on the above 
named islands. : 
I was told, by unquestionable authority, that a rocking 
stone exists in Chilmark, a mile or two south-west of the 
eongregational meeting-house. © But I could not visit it. 
- 3. Plastic Clay Formation. 
cliffs, a series of strata answering to the above description, 
are exhibited usually in great perfection and beauty. Gay 
Head is well known for the bright and variegated colours 
ofits clay, sand and pebble strata ; which present a naked 
sly coloured clays, sand, ferruginous sand, pebbles, 
clay and pebbles, and clay and sand ickanked: e clay 
pees are white, brown, blackish, red, light and deck yel- 
ow, and finely variegated with spots of white, red, and yel- 
