I am not sure. There are a few different things this could be and it can be quite difficult to identify something like this from a photo. Was there something covering these, that you removed before taking the photo? Or were they exposed like that when you found them? 

It was lying along the side, as pictured, when we cranked open our window to clean it.
It was between the edge of the window and the frame inside.
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Ok, thanks. One possibility is that this is a nest of a wool carder bee. They create nest cells from plant hairs and arrange them in a line within cavities. It is pretty common for wool carder bees and other solitary bees to nest in the siding or crevices around windows of homes in the summer. They build the nests within a couple of weeks and then cease all nesting activity until next year.  They are not harmful; in fact they are beneficial in their role as pollinators. You can read more in this article from MSU Extension: https://www.canr.msu.edu/news/michigan-insects-in-the-garden-season-2-week-6-wool-carder-bees
I also have attached a bulletin from Colorado State University that provides some more detail about their nesting behavior. 

Thank you!  I love learning about new species!

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