192 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
grouped in the same horizon or in parallel horizons rather than in 
interwoven bundles. 
(7) Cross-bedding is not a common feature but it occurs in all three 
basins. It has not been observed at Harvard. 
(8) Isolated occurrences of ripple-marks, found in each basin, show 
no inversion of the strata, except possibly in a single case at Brighton, 
where the apparent inversion may perhaps be due to the neighboring 
igneous intrusion. No ripple-marks were seen at Harvard. 
(9) Evidence of contemporaneous erosion is found in all three 
basins and in the Narragansett Basin well-marked examples of local 
unconformity occur. No evidence of this character has been found 
at Harvard. 
(10) The sediments in all three basins were deposited on an old 
surface long subjected to the agents of subaerial disintegration. There 
is no evidence of ancient glacial scoring. The relations at Harvard 
are not clear but no evidence of ancient glaciation has been observed. 
STRUCTURE OF THE CONGLOMERATES. 
Tue Boston Basin.— Literature. Although limited in area, the 
Boston Basin has been made the subject of a considerable literature, 
chiefly, however, in the form of short papers referring to specific fea- 
tures of the basin, or longer papers of broader scope, in which the 
features of the basin are mentioned only incidentally. ‘The Danas 
(1818) speak of the petrographic character of the graywacke; they 
note the size of the ingredients, from rolled masses to grains of sand, 
the relative abundance of quartz and petrosilex, and the less frequent 
occurrence of porphyry, argillite, and “sienite.”” They also speak of 
the character of the cement as consisting not of argillite but of gray- 
wacke, often so fine in grain as to appear homogeneous. President 
Hitchcock (1833) states that the argillaceous slate in the vicinity 
of Boston is intimately associated with the graywacke and probably 
ought to be considered as a variety of that rock. He includes the 
melaphyrs with the graywacke. In 1856 W. B. Rogers announced 
the discovery of Paradoxides harlanı Green at Braintree. 
In the early sixties the controversy as to the nature and origin of 
certain pebbles in the conglomerate arose. President Hitchcock, 
supported by his son, C. H. Hitchcock, from studies at Newport, R. I., 
and at localities in Vermont, contended that the rocks in these places 
show different stages in metamorphism whereby conglomerates and 
