Most likely what you pasted wasn't actually just a block of text; it was a block of text in a table cell. Since table cells can't span pages in Pages, the bottom is cut off. Try this:
Click in your text to select it.
Go to: Format Menu > Table > Convert Table to Text
That should get rid of the table and allow the text to continue on the next page.
I think it's likely in a text box that is big enough to hold all of the text. The bottom of the box would be beyond the bottom of the page. If you used a blank page layout document, any text would automatically be in a text box.
First, go to the template choose & open a new, bland word processing document. If you still have the source of the text copy it again & paste it into this word processing document. If you don't have the original source, you will have to undo the deleting you did on the first document the select all of the text, copy & then paste into the word processing document.