When they occur as beds Interstratified with aqueous strata, they are said to be contemporaneous, because they have evidently been erupted at the time the series of strata among which they appear was being amassed.
"Geology"
James Geikie
The volcanic rocks that overlie the chalk, and some of the strata associated with and Interstratified between masses of basalt, contain leaves of dicotyledonous plants, somewhat imperfect, but resembling the beech, oak, and plane, and also some coniferae of the genera pine and Sequoia.
"The Student's Elements of Geology"
Sir Charles Lyell
It consists, almost purely, of carbonate of lime; the stratification is often obscure, except where rendered distinct by Interstratified layers of flint, a few inches thick, occasionally in continuous beds, but oftener in nodules, and recurring at intervals generally from two to four feet distant from each other.
"The Student's Elements of Geology"
Sir Charles Lyell