It's done deliberately like that as is small viewports there is usually not enough room to show the text but Use this code...
div.layout-fullslideshow .sprocket-features-desc {
display: block ;
}
This is how to create a custom CSS compatible with Gantry 4...
http://docs.gantry.org/gantry4/tutorials/adding-a-custom-stylesheet
Regards, Mark.