MANSFIELD: ROXBURY CONGLOMERATE. 145. 
deposits, but in the normal cycle coarser sediments tend to encroach 
upon and overlie finer. 
:— Estuarine. Willis’s statement (cf., p. 121) is practically a 
Summary of the available data on the bedding of estuarine conglomer- 
ates. The deposits are marked by frequent and irregular interbed- 
ding of coarse sands, sandy clays, and clays, cross-stratified beds, 
ripple-marked and sun-cracked mud surfaces, and channels scoured 
by transitory streams. 
——:— Glacial. In glacial deposits sometimes a rude stratification 
is to be observed in till, and when the layers separate the surfaces. 
usually show a polished or glazed appearance. Sometimes also 
included stratified beds, lenses or pockets of coarse and fine material 
occur. Ordinarily, however, the mass is completely unstratified and 
no assortment of its component materials can be observed. The 
fluvio-glacial deposits have already been noted as possessing all stages 
of stratification up to well-sorted sands and gravels with well marked 
eross-bedding. Where floating ice has dropped glacial debris away 
from shore the boulder-beds thus formed possess a well-marked 
Stratification, as in the case of the deposits of India and New South 
Wales. The bedding may, however, be contorted and confused in 
places where the floating ice masses have stranded or scrubbed along 
the bottom. 
——:—Crush. When true crush-conglomerates are formed the 
crushing movements have often been so intense as to destroy all 
traces of the original bedding. 
Relations to Subjacent Rocks. Rocks of any of the types under dis- 
cussion may rest conformably or unconformably upon underlying 
deposits, with the exception of crush-conglomerates. The latter, 
being the result of mechanical deformation, rather than of deposition, 
can scarcely be considered in this connection, though pseudo-uncon- 
formity may be produced as the result of the overthrust faulting or 
slickensiding of the deformed rock masses. No distinctive character- 
istics have been found to mark the unconformable contacts of the 
other types of rock with underlying masses, save in the case of the 
glacial conglomerates. In all cases cited where the deposits have been 
recognized as being truly glacial, they have been found in some expo- 
Sures to rest upon definitely striated rock surfaces. Helland’s con- 
tention for the glacial origin of the conglomerates in southwestern 
Norway is greatly weakened by his failure to discover such glacial 
markings beneath the rocks in question. 
GENERAL. Discusston.— The details of character and structure of 
